Answer
$5.9$ sec
Work Step by Step
Using the given formula, $d=4.9t^2$, with $d=168,$ thenTaking the square root of both sides (Square Root Property), the equation above is equivalent to \begin{align*}\require{cancel} t&=\pm\sqrt{\dfrac{168}{4.9}} \\\\ t&\approx\pm5.9 .\end{align*} Since $t$ is a measurement (and hence, should be nonnegative), then $t\approx5.9$. Hence, the time, $t,$ for the ball to drop from a height of $168$ $m$ is approximately $5.9$ seconds.
