I'd suggest you enclose -1 and 5 within brackets as shown:
4( 2[-1] - [5] ). Do the work within parentheses FIRST: 4( -7 ).
Then multiply as indicated: -28
Together they picked 10 pints of blackberries.
The reduction was 1/5.
Because you are given the reduced values, multiply the reduced value by the inverrse of the factor:
Inverse of 1/5 = 5
Height = 3 x5 = 15
Base = 5 x 5 = 25
The base is 25
