Answer:
40m (40m east)
Explanation:
The fist move is 70m east, and east is the positive direction so the truck initially is at +70m.
The second move is 120m to the west, since east is the positive direction, west must be the negative direction, this means the truck now is at:
The third move is 90m to the east, again, this is the positive direction, so the new position is:
The truck is at + 40m, so it ended up 40m away from its initial position and this is the resultant dispacement.