Question 301883
{{{ s(t)=-16t^2+144t+272 }}}
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From inspection, we see that the function describes a parabola that opens downwards.  As such, finding the axis of symmetry will give us our answer.
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The axis of symmetry is found by:
x = -b/2a 
x = -144/(2*(-16))
x = 144/(2*(16))
x = 72/16
x = 4.5 seconds