c# - Coordinate conversion - Lat Long to State Plane, ArcServer-Silverlight

I am trying to project a Lat/Long value I get from a table to a x/y value that I can use to plot a graphic.

I have seen one way to do this may be to use something like this:

feature.Geometry = mercator.FromGeographic(new MapPoint(lat, lon));
feature.Symbol = LayoutRoot.Resources["TRUCK"] as ESRI.ArcGIS.Client.Symbols.Symbol;
graphicsLayer.Graphics.Add(feature);

However my graphics aren't showing up overlapping my tiled basemap service. I tried the mercator.FromGeographic and Mercator.ToGeographic with unsuccessful results.

My Lat/Long value: 37.1223133333333,-93.27893

Mercator.FromGeographic converted value: X=-10382795.4374339, Y=4469266.40579955, WKID=102100
Mercator.ToGeographic converted value: X=-0.000837860806483038, Y=0.000334317600035687, WKID=4326

Neither of these coordinates put my graphics in the correct location. It should be closer to something like this: X=1424565.77, Y=501970.98. I am trying to learn more about coordinate systems, conversions between systems, etc. Any thoughts on what I can try next?

I am still in the beginner phase of learning programming so thanks for your help. Would you have this as a standalone class in your project?

Here is the code I have so far:

C#

using System;
using System.Collections.Generic;

using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using ESRI.ArcGIS.Client;

using ESRI.ArcGIS.Client.Geometry;
using ESRI.ArcGIS.Client.Symbols;
using System.Runtime.Serialization;
using ESRI.ArcGIS.Client.Tasks;
using System.Windows.Threading;
using ESRI.ArcGIS.Client.Bing;

namespace TruckGPS_Test
{
    public partial class MainPage : UserControl

    {
        //private static ESRI.ArcGIS.Client.Projection.WebMercator mercator = new ESRI.ArcGIS.Client.Projection.WebMercator();

        public MainPage()
        {
            InitializeComponent();
            //AddMarkerGraphics();

            QueryTask queryTaskTruckGPS = new QueryTask("http://gisaprd/ArcGIS/rest/services/TruckGPS/MapServer/8");
            queryTaskTruckGPS.ExecuteCompleted += QueryTask_ExecuteCompletedTruckGPS;

            ESRI.ArcGIS.Client.Tasks.Query queryTruckGPS = new ESRI.ArcGIS.Client.Tasks.Query();
            queryTruckGPS.OutFields.Add("*");
            queryTruckGPS.ReturnGeometry = false;
            queryTruckGPS.Where = "1=1";
            queryTaskTruckGPS.ExecuteAsync(queryTruckGPS, "initial");

            //This timer updates the outage feature count after a 30 second wait
            System.Windows.Threading.DispatcherTimer myDispatcherTimer = new System.Windows.Threading.DispatcherTimer();
            myDispatcherTimer.Interval = new TimeSpan(0, 0, 0, 10, 0);
            myDispatcherTimer.Tick += new EventHandler(Each_Tick);

            myDispatcherTimer.Start();
        }

        public void Each_Tick(object o, EventArgs sender)
        {
            QueryTask queryTaskTruckGPS = new QueryTask("http://gisaprd/ArcGIS/rest/services/TruckGPS/MapServer/8");
            queryTaskTruckGPS.ExecuteCompleted += QueryTask_ExecuteCompletedTruckGPS;
            ESRI.ArcGIS.Client.Tasks.Query queryTruckGPS = new ESRI.ArcGIS.Client.Tasks.Query();
            queryTruckGPS.OutFields.Add("*");
            queryTruckGPS.ReturnGeometry = false;

            queryTruckGPS.Where = "1=1";
            queryTaskTruckGPS.ExecuteAsync(queryTruckGPS, "initial");
        }

        private void QueryTask_ExecuteCompletedTruckGPS(object sender, ESRI.ArcGIS.Client.Tasks.QueryEventArgs args)
        {
            //If Counter isn't working check the web service, make sure the table is added to the map service

            FeatureSet featureSet = args.FeatureSet;
            GraphicsLayer graphicsLayer = MyMap.Layers["TruckGPS"] as GraphicsLayer;

            graphicsLayer.ClearGraphics();
            if (featureSet != null && featureSet.Features.Count > 0)
            {
                ////Check the system time and subtract the time amount wanted from the last gps systime read for movement or idle truck
                //System.DateTime dTime = DateTime.Now;
                //// tSpan is 0 days, 0 hours, 0 minutes, and 0 seconds.
                //System.TimeSpan tSpan = new System.TimeSpan(0, 1, 0, 0);
                //System.DateTime result = dTime - tSpan;
                foreach (ESRI.ArcGIS.Client.Graphic feature in featureSet.Features)
                {

                    if ((feature.Attributes["LONGITUDE"] != null) && (feature.Attributes["LATITUDE"] != null))
                    //&& (feature.Attributes["S"])
                    {
                        var Machine_Name = feature.Attributes["MACHINE_NAME"].ToString();
                        var User_Name = feature.Attributes["USER_NAME"].ToString();
                        double lat = Convert.ToDouble(feature.Attributes["LONGITUDE"]);
                        double lon = Convert.ToDouble(feature.Attributes["LATITUDE"]);

                        feature.Geometry = new MapPoint(lat, lon);
                        //if (User_Name == "CU656")

                        //{
                        //feature.Geometry = mercator.ToGeographic(new MapPoint(lat, lon));
                        feature.Symbol = LayoutRoot.Resources["TRUCK"] as ESRI.ArcGIS.Client.Symbols.Symbol;
                        graphicsLayer.Graphics.Add(feature);
                        //}
                        //else
                        //{
                        //    feature.Symbol = LayoutRoot.Resources["RedMarkerSymbol"] as ESRI.ArcGIS.Client.Symbols.Symbol;
                        //    graphicsLayer.Graphics.Add(feature);
                        //}

                    }
                }
                { (MyMap.Layers["TruckGPS"] as GraphicsLayer).Refresh(); };
            }
            else
            {
                graphicsLayer.ClearGraphics();
                //MessageBox.Show("No features returned from query");
            }
        }

        private void MyMap_MouseMove(object sender, System.Windows.Input.MouseEventArgs args)
        {
            if (MyMap.Extent != null)
            {
                System.Windows.Point screenPoint = args.GetPosition(MyMap);
                ScreenCoordsTextBlock.Text = string.Format("Screen Coords: X = {0}, Y = {1}",
                    screenPoint.X, screenPoint.Y);

                ESRI.ArcGIS.Client.Geometry.MapPoint mapPoint = MyMap.ScreenToMap(screenPoint);
                if (MyMap.WrapAroundIsActive)

                    mapPoint = ESRI.ArcGIS.Client.Geometry.Geometry.NormalizeCentralMeridian(mapPoint) as ESRI.ArcGIS.Client.Geometry.MapPoint;
                MapCoordsTextBlock.Text = string.Format("Map Coords: X = {0}, Y = {1}",
                    Math.Round(mapPoint.X, 4), Math.Round(mapPoint.Y, 4));
            }
        } 
    }
}

At what point would I use the geometry service or call the class you stubbed out?