Final answer:
In the short run, a firm's total fixed costs can be calculated by subtracting the average variable costs from the average total costs and multiplying that number by the output.
Step-by-step explanation:
In the short run, a firm's total fixed costs can be calculated by subtracting the average variable costs from the average total costs and multiplying that number by the output. In this case, the firm is producing 20 units of output, has average total costs of $200, and average variable costs of $150. So, the total fixed costs can be calculated as follows:
Total fixed costs = Average total costs - Average variable costs * Output
Total fixed costs = $200 - $150 * 20
Total fixed costs = $200 - $3000
Total fixed costs = -$2800
Therefore, none of the options given in the question (a. 10000, b. 500, c. 50, d. 1000) are correct answers for the total fixed costs.