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 $\displaystyle 8$ m long and its cross-section is an isosceles trapezoid which is $\displaystyle 180$ cm wide at the bottom and $\displaystyle 240$ cm wide at the top, and the height is $\displaystyle 60$ 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.