there are 60 minutes in 1 hour, so 1/4 of an hour is 60(1/4), namely 15 minutes.
11:20pm + 4 hours, is 11+4:20, namely 15:20, of course the time system only uses up to 12, so that has to be 3:20, and then we add the 15 minutes.
11+4: 20 + 15.........3:35am.
