Solar energy, Wind energy, Geothermal energy and Hydropower are the renewable resources from which energy is produced and they will never run out because they are produce by nature in large quantity. Solar energy is the energy produced from the sun, Wind energy is the energy produced from the speed of wind, Geothermal energy is the energy produced from the heat of earth and Hydropower is the energy produced due to falling water from higher altitude.
Since it is a cube, all side lengths are the same. So I'm this cafe, all side lengths are 3 ft. So you multiply the depth(3) by the width(3) by the height(3):
