A small pyramid (pointing up) has a square base that measures 15 feet on each side and is 9 feet tall. and is pouring into the pyramid at a rate of .5 ft^3/sec. Express the volumeVof the sand in the pyramid as a function ofh, the height of the sand in the pyramid.

I know that the volume of a pyramid is V = 1/3(h)(b^2). How would I find the relationship between the volume of the sand and the height of the sand given the volume of the pyramid?