Answer:
(c) $10,000
Step-by-step explanation:
If the long-run supply curve is horizontal, then the supply will remain the same in the long-run. The total amount of money (A) that consumers will spend, in total, on potatoes is given by the product of the quantity purchased by the price, and can be found by rearranging the demand function:
Consumers will spend $10,000 on potatoes.