A monopolist has two specific demanders with demand equations: qA = 10 – p and qB = 10 – 2p. This monopolist implements an optimal two-part tariff pricing scheme, under which demanders pay a fixed fee a for the right to consume the good and a uniform price p for each unit consumed. The monopolist chooses a and p to maximize profits. This monopolist produces at constant average and marginal costs of AC = MC.

Question: How to get consumer surplus, pls explain with gram.