Cart 1 has a mass of 15 kg and is moving right at a speed of 2 m/s. Cart 2 has a mass of 5 kg and is moving left at a speed of 3 m/s. When they collide, the carts will stick together. Neglecting friction, what will be the velocity of the carts after the collision?
a) 1 m/s to the left
b) 1 m/s to the right
c) 2 m/s to the left
d) 2 m/s to the right