Answer
(a) $8.4~m/s$ in the positive direction (upward).
(b) $1.4~m/s$ in the negative direction (downward).
Work Step by Step
(a) We know that
$v=v_i-gt$
We plug in the known values to obtain:
$v=28m/s-(9.81m/s^2)(2s)$
$\implies v=8.4m/s$ upward
(b) As $v=v_i-gt$
We plug in the known values to obtain:
$v=28m/s-(9.81m/s^2)(3s)$
$v=-1.4m/s$
The negative sign shows that the speed is directed downward.
