Can someone help me with this question?

One Monopoly Rent Theorem ("1MRT").

1. Assume that a monopolist sells a critical input, "E", at a unit price, "e", to an industry consisting of perfectly competitive downstream firms. The marginal cost of upstream output is 20. It takes one unit of the input to make one unit of downstream output. There are no other variable inputs in downstream production. The downstream industry faces a market demand curve given by Q = 100 - P.

Given this information, what is the profit function of the upstream monopolist?

Find the profit-maximizing level of "e", and calculate the upstream monopolist's profit at that price.