A company that manufactures storage bins for grains made a drawing of a silo. The silo a conical base, as shown below: Which of the following could be used to calculate the total volume of grains that can be stored in the silo?

A. n(6ft)^2 (2ft) + 1/3 n(10.5ft-6ft)^2 (2ft)

B. n(2ft)^2 (6ft) + 1/3 n(10.5ft-6ft)^2 (2ft)

C. n(6ft)^2 (2ft) + 1/3 n(2ft)^2 (10.5ft-6ft)

D. n(2ft)^2 (6ft) + 1/3 n(2ft)^2 (10.5ft-6ft)