The first step is to find the area of the base of the pyramid. Since the base is a square, we use the formula for the area of a square, which is the length of one edge squared. With an edge length of 4 ft, we calculate this as 4 ft x 4 ft = 16 ft². This is the area of the base of the pyramid.
Next, to find the volume of the pyramid, we use the formula for the volume of a pyramid, which is one third of the product of the base area and the height. Substituting the values we have, the volume equals 1/3 x 16 ft² x 15 ft = 80 ft³.
This shows that the volume of the pyramid is 80 ft³. So, the correct answer is C. 80 ft³.