you can see that the height is the same at 0.5sec and 1.5 sec (12ft)
so therefore the height is symmetric about the line t=(midpoint of 0.5 and 1.5)
(0.5+1.5)/2=2/2=1
so the height is symmetric about the line t=1
the ball lands on the ground when height=0
since it is symmetric about t=1, and at t=0, the height is 0
1-0=1, so the difference between symmetry and desired height is 1
we must go in the oposite direction to find the next 0 height
so from symmetry to 0 height is 1+1=2, so at t=2 seconds