A company is introducing a new product. The equation y = –0.001(x – 600)2 + 90 predicts the expected profit, in thousands of dollars, where x represents the number of thousands of units of the product sold by the company. How many units must be sold to yield a maximum profit?

The equation is in vertex form, and its vertex occurs at x = 600. Because the coefficient of the squared term is negative, the parabola opens downward, so this vertex gives the maximum profit. Since x measures thousands of units, 600 means 600,000 units; choice D is correct.

AI-written and checked against the verified answer.