Answer:
F=50kg
D=5m
W=FD
therefore work done is 250Nm
The displacement is the distance from the beginning point to the ending point. The time was just to throw you off. If he walks 30m due west, and then 5m due east, his displacement would be 30-5=25m to the west.
The formula is M=Fd
so we have F=84N and d=0.25m
Now we just replace F and d into the formula M=84N×0.25m
And the last thing we do is calculate it
M=21Nm