I am designing a trapezoidal prism basin that must contain a certain volume per acres contributing to the basin. Therefore, I would like to create a function that will size the basin. My question is: how can I determine the volume between two different areas? In this case these two areas are trapezoids. I know A = a((b1+b2)/2) for area of a trapezoid. Let's say b1 is the smaller side of the trapezoid. In this case trapezoid 1 and 2 will have b11 = b12 while a1 and a2 will not be equal and neither will b21 and b22. I believe that knowing this information will be the key to determining other partial volumes that I will ultimately sum to provide the total volume. Thank you for any help you may have!!