Question 865782
Let {{{ h(t) }}} = the height of the arrow in feet
{{{ h(t)  = -16t^2 + 128t + 100 }}}
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This is a parabola of the form:
{{{ y = ax^2 + b*x + c }}}
If the max height is at ( t[max], h[max] ) 
{{{ t[max] = -b/(2a) }}}
{{{ a = -16 }}}
{{{ b = 128 }}}
{{{ t[max] = -128/( 2*(-16)) }}}
{{{ t[max] = 4 }}}
Plug this result back into equation to get {{{ h[max] }}}
{{{ h[max]  = -16*4^2 + 128*4 + 100 }}}
{{{ h[max] = -256 + 512 + 100 }}}
{{{ h[max] = 356 }}} ft
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Here's the plot:
{{{ graph( 400, 400, -2, 12, -40, 450, -16x^2 + 128x + 100 ) }}}