What magnitude of force, acting for 0.025 s, will change the velocity of a 100 g ball from 30 m/s eastward to 40 m/s westward?
Compute the momentum change and equate it to the impulse (force x time). Then solve for the force.
You may need to review the definition of momentum and how to compute its change. This will be a useful exercise for you. Having someone else do problems for you isn't.