The figure shоws the grаph оf fоur curves. The horizontаl аxis is labeled “Quantity,” and the vertical axis is labeled “Price comma Cost.” The quantities Q sub 0, Q sub 1, Q sub 2, Q sub 3, and Q sub 4 are indicated on the horizontal axis. Q sub 0 is located about one fourth of the way along the axis. The distance from Q sub 1 to Q sub 0 is about one third of the distance between the vertical axis is Q sub 0. The distance from Q sub 2 to Q sub 1 is slightly less than the distance from Q sub 1 to Q sub 0. The distance from Q sub 3 to Q sub 2 is slightly less than the distance from Q sub 2 to Q sub 0. Q sub 4 is just to the right of Q sub 3. The curves are labeled D, M R, M C, and A T C. Curve D begins on the vertical axis, high above the origin, and moves downward and to the right in a straight line until it ends on the horizontal axis, far to the right of Q sub 4. Curve M R begins at the same point as curve D high on the vertical axis, and moves steeply downward and to the right in a straight line until it ends on the horizontal axis at Q sub 1. Curve M C begins about one fourth of the way up the vertical axis, and moves upward and to the right. It intersects curve M R at Q sub 0, intersects curve D at Q sub 3, and ends to the right of Q sub 4, about two thirds of the way up the vertical axis. Curve A T C begins just to the right of, and about half way up, the vertical axis. It moves gradually downward and to the right, crosses curve M R to the left of Q sub 0, and reaches its lowest point where it intersects curve M C at Q sub 2. It then moves gradually upward and to the right, intersects curve D at Q sub 4, and ends far to the right of Q sub 4, just under its initial height. The graph above shows the demand (D), marginal revenue (MR), marginal cost (MC), and average total cost (ATC) curves for a monopoly. Based on the information in the graph provided, what is the profit-maximizing quantity for a monopolist that engages in perfect price discrimination?