Figure 1 shows a squash ball before and after it collides with a wall.

Before the collision, the momentum of the ball is 1.2 kg m/s.
After the collision, the momentum of the ball is 0.9 kg m/s in the opposite direction.
The ball is in contact with the wall for a time of 60 ms during the collision.
Calculate the magnitude of the average force exerted on the ball by the wall.
Use an equation selected from the physics equation sheet.