A vehicle of mass 2.8 t slows from 100. km*h^-1 to 50. km*h^-1 as it enters the city. How much energy could have been recovered, instead of dissipated as heat? To what height, neglecting friction and other losses, could that energy have been used to drive the vehicle up a hill?

The answer is 4.0x10^3 kJ, and 150 m for the second part, but I don't know how they got either. It's a standard kinetic and potential energy problem. Ek=.5*mass*speed, Ep=kg*speed*9.81"acceleration of gravity". Sorry if this seems like a dumb question, but I'm just a beginner, so any help is appreciated.