3. Suppose that a firm's only variable input is labor. The firm increases the number of employees from four to five, thereby causing weekly output to rise by two units and total costs to increase from $3,000 per week to $3,300 per week. a. What is the marginal product of hiring five workers instead of four? b. What is the weekly wage rate earned by the fifth worker? 4. In several perfectly competitive markets for minerals used as inputs in digital devices, persistent increases in demand eventually have generated long-run increases in the market prices of these devices. Describe in words the types of adjustments that must have occurred in these markets to have brought about this outcome, and evaluate whether such mineral-extraction industries are increasing, constant- or decreasing-cost industries