Question about Quadratic equation/parabola/factoring stuff
The Question says:
A model rocket is shot into the air and its ath is approximated by the relation h= -5t + 5t + 30 where h is the height above the ground in metres and t is the time elapsed in seconds.
a) How tall is the building?
This is what I did:
B) WHEN WILL THE BALL HIT THE GROUND?
I thought I could sub h=0 into the equation for this so I did it as follows:
0= -5t^2 -5t + 30
I don't know where to go from here or how to finish the problem or if I did anything wrong. Please help.