Potential energy is a stored energy, which is caused by the gravitational pull of the earth, that is why when you go up the potential energy will increase. to calculate the mass, just substitute the given to the formula and solve for m
PE = m x g x h
4620 = m x 9.8 x 8.4
m = 4620 / ( 9.8 x 8.4)
m = 56.1 kg is thr mass of the man