In a certain physics experiment, carts run along a level, frictionless, one-dimensional track. Furthest to the left is cart A (1 kg) moving at 0.5 m/s to the right. In the middle is cart B (2 kg) moving at 0.2 m/s to the left. Furthest right is cart C (3 kg) moving at 0.4 m/s to the left. (See figure.) They all collide and stick together. Consider the three carts as a system. Take "right" to be positive.
What is the total momentum of the system before the collision?