A hydroelectric power facility converts the gravitational potential energy of water behind a dam to electric energy. (For each answer, enter a number.) (a) What is the gravitational potential energy (in J) relative to the generators of a lake of volume 69.0 km?3 (mass = 6.90 x 1013 kg), given that the lake has an average height of 47.0 m above the generators? (b) Compare this with the energy stored in a 9-megaton fusion bomb. ; X