Two cars are driving along Robinson Street during an ice storm when they hit a patch of ice. The car in front is traveling at a speed of 8.0 m/s when it starts sliding and the car in back is traveling at a speed of 17.0 when it starts sliding. The back car has twice the inertia (mass) of the front car. When the back car hits the front and the bumpers lock, how fast will the two cars be moving?