Please answer both parts and provide the correct answer. Tried using ChatGPT for assistance/explanation but I don't think the steps and answer were correct.

A particle of mass M decays into three particles with different masses, M = ma+mp+ me. a) Find the maximum energy of particle A in the rest frame of M. b) Repeat part a) in the frame where the initial three-momentum of particle M is P. You may express your answer in terms of the maximum energy and momentum of particle A in the rest frame of M