I think what you need to do here is do the volume of a cone. Which is 1/3 pir^2h. The first step is to find the radius. In order to do that is to divide the diameter by 2. You do this because the radius is two times smaller than the diameter. Then you want to multiply the radius (which is 6 inches) by the height (12 inches). By this time you should have the number 72 (12x6). The next step is to multiply 72 by pi, or 3.14. Which is 226.08. I hope that you realized that all is left in the formula is the fraction 1/3. What you do here is divide the sum, or what you have multiplied. So, 226.08 divided by 3 is 75. 36. The model should be 75.36 inches.
