Got it. Also I proved in part a that P was a group so does that cover point one enough? Or do I have to do it again just for additionHave to use letters. p and q have to represent ANY element of P. If you use examples you can show it, sure, but all that means is that the proof holds for those examples. It means nothing for the entire group.
Also, use the function symbol given to you so you avoid confusing the grader, if there is one. φ