7. A monopolist has cost function  =  + 2 and the regulator is willing to allow the firm to use a two-part tariff per consumer  =  +  to cover total costs. Total demand is  = 102 −  and there are 100 identical consumers. Up to how much is willing to pay each indidual consumer to have the right to consume the good at marginal cost? What is the optimal tariff or tariff that would maximize social welfare (fixed part and marginal price) ?