You could plug each answer choice into the formula along with the given information and see which answer works.
***It helps to have a calculator do the quick calculations
A) r = 3 cm → 300 = [tex] \frac{1}{3} \pi * 3^{2} *10[/tex] ≈ 94.2 NOT IT
B) r = 5 cm → 300 = [tex] \frac{1}{3} \pi* 5^{2} *10[/tex] ≈ 261.7 THE CLOSEST
C) r = 9 cm → 300 = [tex] \frac{1}{3} \pi* 9^{2} *10[/tex] ≈ 848.2 NOT IT
D) r = 28 cm → 300 = [tex] \frac{1}{3} \pi* 28^{2} *10[/tex] ≈ 8210.02 NOT IT
