Arturo O. answered • 09/07/18

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h(t) = -16t

^{2}+ 108t + 28(a)

Maximum height occurs at the vertex of the height-vs.-time parabola, which is at

t = -108/[2(-16)] sec = ? sec

Evaluate h(t) at this value of t to get h

_{max}.(b)

Set h(t) = 0 and solve the quadratic equation for t. You will get a positive and a negative solution. Discard the negative solution, since time starts at t = 0.

You have all you need to finish from here.