The first thing to do is work from a 24-hour clock. 2:48am is 0248 and 7.14pm is 1914.
Next, to make the calculation easier, we work out the hours between 0248 and 1948. That's 17 hours (19-2).
Now the minutes. It's 17 hours up to 1948, so we need to subtract the minutes: 48-14=34 minutes. It's 17 hours less 34 minutes=16 hours and 26 minutes (60-34=26 minutes).