This is a truncated cone.
Which means we can use the following formula:
π × h × (R²+r²+R×r) ⁄ 3
Where R is the upper radius, and r the bottom radius.
3 is used as PI in this case.
3 * 10 * ((11/2)^2 + (13/2)^2 + (11/2)(13/2))/3
30*108.25/3
Which is (almost) equal to:
30*36
or, as your teacher put it:
10 * 3 * 36
Hence,
C is the best answer :)
