In a competitive market, a firm believes that it can sell as many units of the good as it wants by setting a price less than or equal to the market price. Then there is no reason to put a price lower than the market price. In other words, the firm should desire to sell some amount of the good, the price that it sets is exactly equal to the market price. A firm earns revenue by selling the products it produces in the market. Let the market price of a unit of interest be p. If q be the quantity of the good produced, and sold, by the firm at price p. So, the total revenue (TR) of the firm is defined as the market price of the good (p) multiplied by the firm's output (q). Hence, TR = p × q.