help? A crayon is shaped like a triangular prism. The base of the crayon is shown. If the crayon is 90 millimeters long, how many cubic millimeters of wax is used to make a box of 8 crayons?

Answer is 69.12 cm³
I had explained it but deleted it all cuz I thought I got it wrong but I was correct and class starts so I don't have time to explain