Question 82299
s(t)= -16t^2+64t+80
When the ball is at ground-level s = 0.
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EQUATION:
-16t^2+64t+80 = 0
-16(t^2-4t-5)=0
t^2-4t-5=0
(t-5)(t+1)=0
Positive answer: t=5 seconds
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Cheers,
Stan H.