An meson decays into 2 while moving in the x direction with energy E =

An η meson decays into 2γ while moving in the x direction with energy E_η = 5 GeV.
(1) If the two γs are emitted in the +x and -x directions, what are their energies?
(2) If the two γs are emitted at equal and opposite angles  ±θ with x, what is the angle between the two.