Question 53784
h=8t-t^2 
Q. find after what time the ball is first at a height of 12m
Let the height be 12m and solve for "t" as follows:
12=8t-t^2
t^2-8t+12=0
(t-6)(t-2)=0
t=2 seconds is the 1st time the ball is at 12m
Cheers,
Stan H.