multiple choice?

Question

A farmer has decided to build a pen for his horse alongside a drainage canal. If the pen is to be rectangular in shape and he has 400 feet of fencing available, what is the area of the largest possible pen he can create? He doesn't need to have fencing on the canal side of the pen.

A) 400 ft^2
B) 10,000 ft^2
C) 20,000 ft^2
D) 40,000 ft^2
E) None of the above

explanation???

Answer 1

100 by 200 by 100 with the fourth side the canal, "C"

Answer 2

a) 400ft^2