Keira created color panels for a wall using a mix of only red and blue paints. She plotted the quantities of red and blue paints used for each mix and connected them using a line segment, as shown in the graph below:
A line graph titled Color Mix, with Quantity of Blue Paint, in millimeters, on the X axis and Quantity of Red Paint, in millimeters, on the Y axis. The X axis has a scale from 0 to 9 with an increment of 1. The Y axis has a scale of 0 to 18 in increments of 2. A straight line connecting 3, 2 and 7, 12 is drawn. Which statement best describes the domain of the function represented in the graph? (1 point)