A Firm Produces Heavy Machinery and Can Sell 10 Units

A firm produces heavy machinery and can sell 10 units per month at a price of $50,000.To increase sales to 11 units per month,the firm must cut its price to $46,000.The marginal revenue for selling one extra unit per month is

A) $363.
B) $4,000.
C) $4,182.
D) $6,000.
E) $46,000.