The professor told us we would have similar ones on our midterm and we need to understand how to solve this type of problems.

I need help solving this lengthy and complicated problem. The professor told us we would have similar ones on our midterm and we need to understand how to solve this type of problems. I got confused right in the beginning and as all questions are connected I'm not sure how to solve it at all... Your help is highly appreciated. Thank you!

2 firms compete in prices, demand function is Q = 36 P (Q - total output traded in the market, P- market price that is given by the lowest price set by a competing firm). Both firms have constant marginal