The volume of a pyramid is V=1/3Bh (One-third the area of the base times height). Since your pyramid has a square base, you have to find the area of the base, multiply it by the height, and then divide it by 3.
So, the area of the base is 4x4, which is 16, then you multiply it by the height, 5, and 16x5 is 80, and 80/3 is approximately 26.6
The answer would be 26.6 cm^3