The only variable input a janitorial service firm uses to clean offices is workers who are paid a wage, w, of $8 an hour. Each worker can clean four offices in an hour. Use math to determine the variable cost, the average variable cost, and the marginal cost of cleaning one more office. Draw a diagram similar to Figure 7.1 to show the variable cost, average variable cost, and marginal cost curves?

Figure 7.1: Short-Run Cost Curves