Quick questions on Time zones and time differences (QCE General Mathematics Unit 3)

The Sun rises in the east, so a place to the east experiences a later local time (it is ahead). A place to the west is behind. When moving east you add the time difference; when moving west you subtract it. This is the single rule that decides the sign of every answer.

To find the difference between two locations, find the gap between their longitudes (add if on opposite sides of the prime meridian, subtract if on the same side), then divide by $15$ to convert degrees to hours.

Roughly along $180\degree$ longitude lies the International Date Line. Crossing it from east to west advances the calendar by one day; crossing from west to east goes back one day. In General Mathematics questions you usually only need to note that a long westward trip can land you on the next calendar day.

A typical question gives a departure local time, a flight duration, and the two longitudes. The method is: convert the longitude gap to a time difference, adjust the departure time to the destination's local time, then add the flight duration. Keep the time-zone adjustment and the flight time as separate steps.