The market demand curve for mineral water is P=a-bQ. Suppose that there are two firms that produce mineral water, each with a constant marginal cost of c dollars per unit. Fill in the entries for each of the following duopoly models. Bertrand model (Price competition). Cournot model (quantity competition). Collusion.

Can someone show me their algebra on each step. I think Im getting the MR incorrect. Does Q=Q_1+Q_2?