somebody please help

Easy pickings

 

First we find the area of the big triangle (the one that has both the not shaded and the shaded)

 

20^2=400

 

400/2=200

 

Next we should find the area of the not shaded triangle.

 

15x10=150

 

150/2=75

 

200-75=125

 

Yay!

Area of large triangle - area of smaller triangle

1/2  20 * 20      -   1/2  10 * 15   =    shaded area