A mass of 3 kg is moving in the +x direction and collides inelastically with another mass of 9 kg moving at 4 m/s in the -x direction. The collision...

A mass of 3 kg is moving in the +x direction and collides inelastically with another mass of 9 kg moving at 4 m/s in the -x direction. The collision takes place in 0.21 seconds and the average force on the second mass is 161 Newtons in the +x direction. What is the kinetic energy of the 3 kg mass before the collision?