Atrack-and-field athlete releases a javelin. the height of the javelin as a function of time is shown on the graph below.

The given graph is parabola graph with vertex at the point (2.0,24) and branches of the parabola go in a negative direction of y-axis. 
As known parabola is symmetric about her axis of symmetry and in this case the symmetry axis has equation t=2.0 (vertical line). Thus, the height of the javelin above the ground is symmetric about the line t=2.0.

From the graph you can see that the first time when javelin is 20 feet above the ground is when t=1.0 and the second time is t=3.0 (to determine this you should draw horizontal line through point (0,20) and consider two points of intersection (1.0,20), (3.0,20) between parabola and horizontal line).

put like terms together.orremember that the 45 becomes negative when moved to the other side.orthe minuses cancel out.