Water Trough Practical Application

A 10ft long trough whose sides are shaped like isosceles triangles with a height of 1ft and a base of 3ft, fills up with water at a rate of 12 cubic feet per minute. How fast is the water rising when the water is 6 inches deep?

I created an excel spread sheet that illustrates whats going on here very nicely. But I'll leave one hint right here. The key is to write an equation that relates the depth of the water to the volume of the water. Follow the link to download the xls file.

WaterTroughProblem.xls