I believe it’s 9x+1
Add all the equations/side values together
Plug in f(t) = 0. We do this because f(t) represents the height and a height of 0 means you're at the ground.
f(t) =-5t^2 + 20t + 60
0 = -5t^2 + 20t + 60
-5t^2 + 20t + 60 = 0
Now solve for t using the quadratic formula