During a training exercise, a rescue team raises a stretcher of mass 20 kg. The gravitational potential energy of the stretcher increases by 800 J. Use g=10 N/kgg=10\ \mathrm{N/kg}g=10 N/kg. Through what vertical height is the stretcher raised?
80 m80\ \mathrm{m}80 m
40 m40\ \mathrm{m}40 m
0.25 m0.25\ \mathrm{m}0.25 m
4.0 m4.0\ \mathrm{m}4.0 m