Question 1158980
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<pre>

For it, you need to solve this quadratic equation


    -16*t^2 + 80t + 6 = 0.

Or

    16*t^2 - 80t - 6 = 0


    {{{t[1,2]}}} = {{{(80 +- sqrt(80^2 - 4*16*(-6)))/(2*16)}}} = {{{(80 +- 82.365)/32}}}.


You do not need negative root - it makes no sense.


You need only positive root  t =  {{{(80 + 82.365)/32}}} = 5.074.   (rounded)


<U>ANSWER</U>.  5.074 seconds.
</pre>

Solved.