I can't solve this problem too! Please help me! I am taking exams next week and i 'm supposed to know what happens! my prof gave us a little help by saying these:
1). 1239.8/E=... (and i think from this we have λο)
2). ΔΕ -> Εφ=Εφ'+Εmax(e) -> 50keV=Εφ-Εφ' (where Eφ=photon's energy)
3) θ=π...