Question 304263
{{{h(t)=-16t^2+70t+75}}}
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Set h(t) to zero and solve for t:
{{{0 = -16t^2+70t+75}}}
{{{0 = -16t^2+70t+75}}}
Solve by applying the quadratic formula.  Doing so will yield:
t = {-0.9, 5.3}
We can toss out the negative solution leaving:
t = 5.3 seconds
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Details of quadratic formula to follow:
*[invoke quadratic "x", -16, 70, 75 ]