Question

a 95 kg fullback is running at 4 m/s and is stopped in .75 s by a tackle from a head on tackle from the opposite direction.
I found the original momentum of the fullback (380 kg m/s), the impluse exerted on the fullback (-380 kg m/s), and the impluse exerted on the tackler (380 kg m/s), but don't know how to find the last piece of the problem: the average force exerted on the tackler.