Question 1004044
The father using one wall and 40ft. of fencing:
-this means the fence will need to cover 3 sides. 40/3=13, r.1
-this puts each wall at 13ft
-lengthXwidth=area, so 13x13=169
-FATHER CAN ENCLOSE 169 SQUARE FEET

The son using two walls and 40 ft. of fencing:
-this means the son's fence must only cover 2 of the sides
-40/2=20, this puts each wall at 20ft.
-20x20=400
-SON CAN ENCLOSE 400 SQUARE FEET

Hope I helped :)
-rosey51235