I have been working on this problem for quite awhile now and I can't seem to get the right answer.

A water trough is m long and its cross-section is an isosceles trapezoid which is cm wide at the bottom and cm wide at the top, and the height is cm. The trough is not full. Give an expression for V, the volume of water in the trough in cm^3, when the depth of the water is d cm.