An electron (rest mass me) of energy E makes a head-on collision with a positron (positron is electron's antiparticle, it has the same mass as

An electron (rest mass me) of energy E makes a head-on collision with a positron (positron is electron's antiparticle, it has the same mass as electron, but opposite charge) In collision the two particles annihilate each other and are replaces by two photons (γ rays) of equal energy, each traveling at equal angles θ with electron's direction of motion. Find 1. The energy of each photon. 2. The momentum p of each photon. 3. The angle θ.