Answer: C. 12 inches
Step-by-step explanation: Let's use the formula for the volume of a cylinder, which is:
V = πr^2h
where V is the volume, r is the radius, and h is the height.
We ar given that the length of the radius is twice the height, which can be written as:
r = 2h
We are also given the volume of the cylinder, which is 864 cubic inches. Substituting the given values, we get:
864 = π(2h)^2h
Simplifying and solving for h:
864 =4πh^3
h^3 = 864/(4π)
h = 6
Now that we know the height of the cylinder is 6 inches, we can find the radius using the equation r = 2h:
r = 2(6) = 12 inches
Therefore, the length of the radius of the cylinder is 12 inches, which is option C.