Answer
(a) $W=-3381J$
(b) $W=3381J$
Work Step by Step
Since the velocity is constant, gravitational force equals normal force exerted on the man. In other words, $$F_N=mg=75\times9.8=735N$$
(a) Since the elevator is moving upward, $mg$ and $s$ point in opposite direction, so $\theta=180^o$
$$W=(mg\cos180)s=-3381J$$
(b) We have magnitude of displacement $s=4.6m$ and the normal force by the elevator, which is $F_N=735N$. $F_N$ and $s$ point in the same direction, so $\theta=0^o$
$$W=(F_N\cos0)s=3381J$$
