For this case we have the following equation:

To solve we follow the steps below:
We add similar terms from the left side of the equation:

We divide between 6 on both sides of the equation:

Finally, we have to:

Answer:

Answer is 120 in^3
Reason
Cone volume is 1/3 BH
(or 1/3 volume of a cylinder)
1/3 x 36 x 10
Answer = 120
If you're finding diameter or radius based on circumference, use the formula C = πd. You would divide the circumference by pi to get the diameter, then divide the diameter by 2 to get the radius.
If you're finding diameter or radius based on area, use the formula A = πr^2. You would divide the area by pi, then find the square root of that value which is the radius. Just multiply the radius by 2 to find diameter.