Quick questions on Local time and the International Date Line for HSC Maths Standard 2

Each place is a fixed number of hours from UTC. To find how far apart two places are, subtract one offset from the other and take the size of the answer. For Sydney at UTC $+10$ and Los Angeles at UTC $-7$,

Once you know the difference and which place is ahead, convert a time by adding the difference to go to a place that is ahead, and subtracting it to go to a place that is behind. Suppose it is $2{:}00$ pm in Sydney and you want the time in Los Angeles. Los Angeles is $17$ hours behind, so subtract $17$ hours. Working in $24$-hour time, $2{:}00$ pm is $14{:}00$, and

The world's time zones are measured east and west from UTC, and they meet on the far side of the globe at the International Date Line, which runs roughly down the $180\degree$ meridian in the Pacific Ocean. The date line is where each new calendar day begins, so crossing it changes the date by a whole day:

A flight problem combines three pieces: the departure time, the flight duration, and the zone change. The reliable method is to work in $24$-hour time and apply them in one running sum: