Refer to exhibit 24-9. a single-price monopolist that seeks to maximize profits will sell units and charge a per-unit price of

A single-price monopolist sells the same price to its customers and does not practice price discrimination. He/She is a price setter. By the way, is the attached picture the Exhibit you are referring to?
A single-price monopolist that seeks to maximize profits will sell 10 units and charge a per-unit price of $10.

Just divide the x axis (the top) by 2 or multiply the y axis (the bottom) by 2