When it hits the ground, h = 0 ......so.....
-10t^2 + 10t + 60 = 0 multiply through by -1
10t^2 -10t - 60 = 0 divide through by 10
t^2 - t - 6 = 0 factor
(t - 3) ( t + 2) = 0
The first factor set to 0 gives us what we need
t - 3 = 0
t = 3 (seconds to hit the ground)