A neutron with a mass of 1.67 × 10-27 kg traveling east with a kinetic energy of 2.00 × 10-21 J collides perfectly elastically with a helium nucleus with a mass 6.68 × 10-27 kg that is initially at rest. After the collision, the neutron has a kinetic energy 1.80 × 10-21 J. What angle was the neutron deflected during the collision? I am able to calculate the values of the final velocities. I just don't know what to do with the information provided and the information I calculated to get the final angle of deflection.