Ben is building a storage box for the sail of his boat. The left side of the box is 3 feet long and the right side of the box is 4 feet long. The left and right side form a right angle, as shown in the picture below.What is the length of the base of the box?
A.
4.5 feet
B.
7 feet
C.
5 feet
D.
3.5 feet