You throw a ball upward. its height h in feet after t seconds can be modeled by the function h=-16t^2+30t+6.after how many seconds will it hit the ground

When the ball hit the ground, the height will be equal to "0".
h=0
Then:

-16t²+30t+6=0

we have to solve this square equation:

t=[-30⁺₋√(900+384)] / (-32)
t=(-30⁺₋√1284)/(-32)
we have two solutions:
t₁=(-30-√1284)/(-32)=2.06
t₂=(-30+√1284)/(-32)=-0.18  This solution is not valid.

2.06 seconds.
t

Where is the graph function?