Question is too big, however, I desperately need help plz?

The uranium-235 nucleus is stationary at the time that the fission reaction occurs. In this fission reaction, 198 MeV of energy is released. Of this total energy, 102 MeV and 65 MeV are the kinetic energies of the strontium-90 and xenon-142 nuclei respectively. Sorry, but i forgot to include the nucleons and protons. Uranium is (235 and 92). Strontium is (90 and 38) and xenon is (142 and 54)

(a) Calculate the magnitude of the momentum of the strontium-90 nucleus and explain why the magnitude of the momentum of the strontium-90 nucleus is not exactly equal in magnitude to that of the xenon-142 nucleus.