The volume of a pyramid varies jointly with the base area of the pyramid and its height. The volume of one pyramid is 24 cubic inches when its base area is 24 square inches and its height is 3 inches. What is the volume of a pyramid with a base area of 15 square inches and a height of 7 inches?

I think they mean something like:

V = A*base_area*height, with A some constant. Indeed, A=1/3, but it does not really matter here.

You may take ratios:

V_2/V_1 = base_area_2*height_2 / (base_area_1*height_1)

So, V_2/24 = 15/24*7/3 - - > V_2 = 24 * 15 * 7 / 24 / 3 = 35 cubic inches

This way of taking ratios of functions with some dependencies is good to know because it is asked several times.