Getting information from one shapefile to another using QGIS

I am very new to GIS and learning by myself.

I am using QGIS.

I have a shapefile, which categorizes areas (land cover) by numbers (corresponding to land cover classes).

I have created a wkt file with twelve polygons, with the following structure: id|polygon

e.g.:

150-180|POLYGON((559053 4367372,559053 4364372,557553 4366970.07621135,559053 4367372))

120-150|POLYGON((557553 4366970.07621135,559053 4364372,556454.923788647 4365872,557553 4366970.07621135))

90-120|POLYGON((556454.923788647 4365872,559053 4364372,556053 4364372,556454.923788647 4365872))
....

The polygons from the wkt file superimpose categorized areas from the shapefile.

I wish to know the following: how much of each category (from the shapefile) is included in each polygon from the wkt file?

e.g.:

150-180: 0.25 of the area is category 232 + 0.70 of the area is category 123 + 0.05 of the area is category 657

How can I do this?