Sydney, Australia is 13 hours ahead of my current location. If it's 3:00 pm here, what time is it in Sydney, Australia?
4am the next day
I'm going to use a 24-hour clock for this question to eliminate the whole "AM/PM" thing.
It's "3pm here" - which in a 24 hour clock is 15:00.
Australia is 13 hours ahead - so we add 13 hours:
Since the result is greater than 24, we've advanced a day. We subtract 24 hours to get the time: