Answer
$t \approx 4.1$ seconds
Work Step by Step
$s(t) = -16t^{2} + 64t + 5$
$-16t^{2} + 64t + 5 = 0$
$t = \frac{-(64)±\sqrt {(64)^{2}-4(-16)(5)}}{2(-16)}$
$t = \frac{-64±\sqrt {4096+320}}{-32)}$
$t = \frac{-64±\sqrt {4416}}{-32}$
$t = \frac{-64±8\sqrt {69}}{-32}$
$t = \frac{-32±4\sqrt {69}}{-16}$
$t = \frac{16±2\sqrt {69}}{8}$
$t = \frac{8±\sqrt {69}}{4}$
$t = 4.0765...$ seconds
$t \approx 4.1$ seconds