A roller coaster (491 kg) moves from A (1.09 m above the ground) to B (26.3 m above the ground). Two non-conservative forces are present: friction does -2.39 x 104 J of work on the car, and a chain mechanism does +5.18 x 104 J of work to help the car up a long climb. What is the change in the car's kinetic energy KEf - KEo from A to B?