Evan is landscaping his backyard. The yard is shaped like a rectangle and measures 80 feet by 70 feet. He wants to spread topsoil evenly over the entire surface. One load of topsoil will cover 400 square feet, 4 inches deep. How many loads of dirt does Evan need in order to cover his entire yard?
A. 14
B. 16
C. 18
D. 20