Final answer:
The marginal revenue of the tenth garage is the difference in total revenue when selling 10 units versus 9 units. This comes out to be $1,000, making the correct answer D. $1,000.
Step-by-step explanation:
The marginal revenue of the tenth unit is the additional revenue the firm would earn by selling the tenth unit. This is calculated as the difference in total revenue from selling 10 units instead of 9. Selling 10 units at $10,000 each gives a total revenue of $100,000, whereas selling 9 units at $11,000 each gives a total revenue of $99,000. Therefore, the marginal revenue of the tenth unit is:
Total Revenue at 10 units - Total Revenue at 9 units
$100,000 - $99,000 = $1,000
Hence, the correct answer is D. $1,000.