A Manufacturer Sells Watches for $75 Per Unit

Multiple Choice

A manufacturer sells watches for $75 per unit. The fixed costs related to this product are $10,000 per month, and the variable costs are $55 per unit. This gives a profit function , where r is the revenue per unit and c is the variable cost per unit. If the manufacturer has a profit of zero, how many watches were sold? ​

A) 1,000
B) 5,000
C) 500
D) 133
E) 182