Trisha - this problem is virtually identical to the "pile of ore" problem we worked on earlier.
In the pile of ore problem, there were triangles at the two ends and trapezoids at the two sides. This problem is the same except we replace the two triangles with trapezoids.
Use the same formula for the volume of a prismatoid:
Now, plug the results into the volume formula:
Convert to yards (1 yard = 3 feet):
Hope that helped