The height of the javelin above the ground is symmetric about the line t = seconds. the javelin is 20 feet above the ground for the first time at t = seconds and again at t = seconds

I FOUND YOUR COMPLETE QUESTION IN OTHER SOURCES.
 PLEASE SEE ATTACHED IMAGE.

 Part 1:

 we must see in the graph the axis of symmetry of the given parabola.
 The axis of symmetry is the following vertical line:
 
 
 The height of the javelin above the ground is symmetric about the line t = 2 seconds:

 Part 2:

 we must see the time t for which the javelin reaches a height of 20 feet for the first time.
 We have that when evaluating t = 1, the function is:
 
 To do this, just look at the graph.
 Then, we must observe the moment when it returns to be 20 feet above the ground.
 For this, we have from the graph that:
 
 Therefore, a height of 20 feet is again reached in 3 seconds.
 
 The javelin is 20 feet above the ground for the first time at t = 1 second and again at t = 3 seconds