Profit Maximizing Under Monopoly. The inverse market demand for mineral water is P = 130 - Q, where Q is the total market output and P is the market price. One firm, A Industries, has complete control of the supply of mineral water. Marginal costs are constant and equal to 10 (i.e. MC=10) Draw a graph that shows demand, marginal revenue, marginal cost, the profit-maximizing level of quantity and price, and indicate the area of profit.