A silo is a composite of a cylindrical tower with a cone for a roof. What is the volume of the silo if the radius of the base is 40 feet, the height of the roof is 10 feet, and the height of the entire silo is 75 feet?

a. 393,746.3 ft
b. 343,480.8 ft
c. 326,725.6 ft
d. 376,991.1 ft