Removing extra string from text column in Attribute Table to make numeric column from number part using ArcGIS Field Calculator?

I received a shapefile about invasive species. I am using ArcGIS 10.2 for desktop. In Attribute Table, there is column called "Infested_Area" and its got number mix with text, for instance "9100 sq feet". Since I can not run statistic on string I was wondering if it's possible to create a new filed and somehow get rid of the text portion of it and only have number!

Answer

This is similar to @PolyGeo solution

but will handle different units and unitless entries

!TextField!.split(" ")[0]

Note you cannot run statistics on result, if units are different