The answer is c because you take the formula of the circumference, c=2rpi, set it equal to 10pi. Then you find r. When you find r it should be 5. Next you put that 5 into the formula for volume, v=r^2*pi*h, and set it equal to you volume, then solve for v.
300pi = 5^2 *pi* h
300pi = 25pi * h
300pi/25pi = h
H = 12