[5] Currently operating at an output level of 8 units, a purely competitive firm faces a market price of $100 and an average total cost of $50. If the marginal cost of the 9th unit of output is $90, then as this firm expands its production to 9 units, profit will to A. B. C. D. rise; $1000 rise; $410 rise; $510 fall; $90

[5] Currently operating at an output level of 8 units, a purely competitive firm faces a market price of $100 and an average total cost of $50. If the marginal cost of the 9th unit of output is $90, then as this firm expands its production to 9 units, profit will to A. rise; $1000 B. rise; $410 C. rise; $510 D. fall; $90