For the graph whose function is shown below, find when . Enter the answers as x=n,m. A graph on the Cartesian coordinate plane showing a concave-down parabola. The vertical axis is labeled f of x. The y-intercept has coordinates (0,21). There are two x-intercepts, (3,0) and (7,0). Other points labeled on the graph include (2,9), (6,9), (2,25), and (4,21). X=_________