Please help me with this physics problem! Show all work and explain! Thank you! Draw body diagram if needed

1. A horizontal spring of spring constant k is attached to a wall. A mass m compresses the spring a distance D. You let go of the mass. The spring shoots out the mass, which moves along a horizontal frictionless surface. It strikes a second mass m and stick to it.

a) How fast are the two stuck masses m moving out at the end of the problem?

b) If the collision lasted a time , what was the average force with which the second mass pushed on the first mass during the collision?