4. Let y = x be a production function relating input x to output y. Let & represent the unit cost of input x, and assume that total cost equals fixed costs, Co, plus the cost of input x. Let p be the unit price of y. Find the revenue function, the cost function, and the profit function for the firm. Given that the function f(x) = x is continuous, are these functions continuous? (Use theorem 4.1 to answer this question.) Discuss.