A 1200-kg car and 2500-kg truck are sliding toward each other across a sheet of ice. The car is noving at 13.5 m/s to the right, while the truck is moving at 7.8 m/s to the left. Something happens, and afterwards the car is moving to the left at
3.4 m/s. If momentum is conserved, what is the new speed in m/s) of the truck?