Answer
Please see the work below.
Work Step by Step
We know that
(a) $v_f^2-v_i^2=-2g(\Delta y)$
We plug in the known values to obtain:
$(0)^2-v_i^2=-2(9.8)(4.2-1.5)$
$v_i=7.3\frac{m}{s}$
(b) As $y=y_{\circ}+v_{\circ}t-\frac{1}{2}gt^2$
We plug in the known values to obtain:
$(4.2-0.87)=1.5+(7.275)t-\frac{1}{2}(9.8)t^2$
$t=1.2s$
