Answer
See explanation.
Work Step by Step
By symmetry, the two photons have equal energies.
a. Each photon has the rest energy of a proton.
Each photon has energy of 938.3 MeV.
Frequency $f=\frac{E}{h}=2.27\times10^{23}Hz$.
Wavelength $\lambda=\frac{c}{f}=1.32\times10^{-15}m$.
b. Each photon has the rest energy of a proton, 938.3 MeV, plus the KE of 620 MeV.
Each photon has energy of 1558 MeV.
Frequency $f=\frac{E}{h}=3.77\times10^{23}Hz$.
Wavelength $\lambda=\frac{c}{f}=7.96\times10^{-16}m$.
