A skateboarder collides with a ball (PhysCasts)

This PhysCast looks at objects colliding and how to analyse them in terms of momentum. A child on a skateboard is moving along a horizontal surface at 5.0 m/s, when they collide with a rubber ball rolling towards them at 3.5 m/s. The ball has a mass of 2.2 kg, and after the collision is moving at 6.0 m/s opposite to its intial motion. The combined mass of the child and their skateboard is 45 kg. What is the velocity of the skateboarder after colliding with the ball