A hiker of mass 76kg is going to climb to the top of Mount Tam, which has an elevation of 2574 ft. If the hiker starts climbing at an elevation of 325 ft, what will the change in gravitational potential energy be, in joules, once they reach the top? Assume the zero of gravitational potential energy is at sea level. Repeat the above calculation for the change in gravitational potential energy, but assume the gravitational potential is zero at the top of the mountain.