Exercise 1: sample answer

It is local noon at the ship while the Greenwich clock reads 15:00. The ship's time is therefore three hours behind Greenwich's. Time runs later towards the east, so a place whose clock is behind Greenwich's lies to the west.

Three hours at 15 degrees an hour is 45 degrees, so the ship is at about 45 degrees west of Greenwich (check against a map: this is in the mid-Atlantic).

Rule of thumb: ship's time behind Greenwich means west; ahead means east.