On Monday at 2:00 pm local time in Sydney (+10h), an email is sent to Rio de Janeiro (-3h). At what local time in Rio de Janeiro should the email arrive? You may assume that the email arrives instantly.
Sydney is 10 hours ahead of UTC and Rio is 3 hours behind UTC
10 + 3 = 13
so there is a 13 hour time difference.
We have to count backwards from 2pm by 13 hours which makes it 1am in Rio