Answer
Please see the work below.
Work Step by Step
We know that
(a) $h=\frac{v^2}{2g}$
We plug in the known values to obtain:
$h=\frac{(23)^2}{(2)(9.8)}$
$h=27m$
(b)$t=\frac{v_f-v_i}{-g}$
We plug in the known values to obtain:
$t=\frac{(-23)-(23)}{-9.8}$
$t=4.7s$
