submit the answer and then watch the video feedback. A graph of three curves plots the relationship between price P on the vertical axis and quantity on the horizontal axis. An upward sloping marginal cost curve M C intersects a U-shaped average variable cost curve A V C at the minimum of the A V C at the point (50, $7) and a U-shaped average total cost curve A T C at the minimum of the A T C at the point (65, $10). The A V C curve lies completely below the A T C curve. Three horizontal lines extend from the vertical axis, one at $7 that touches the intersection between A V C and M C at quantity 50, one at $9 that intersects M C at quantity 60 and A V C at quantity 75, and one at $10 that touches the intersection of A T C and M C at quantity 65 and intersects A V C at an unlabeled point beyond 75. What is the firm's profit-maximizing quantity of output when the price is $9? a. 50 b. 60 c. 65 d. 75