The volume of a pyramid is the area of the base * the height.
Given that it is a square pyramid, its base is a square.
As per your data (you didn't include the picture), the area of the base will be (24ft)^2 and height is 20 ft.
So,m the volume of the pyramid will be (24ft)^2 * 20 ft = 11,520 ft^3.
That result is not one of the options, so the data provided are not those of this problem. But with this explanation now you know how to use the actual data and calculate the volume of the square pyramid.