Answer :
If the baby went to sleep at 9:30 and woke at 2:45.
Then the baby slept 5 hours and 15 minutes.
Just start at 9:30 and skip count 9:30, 10:30, 11:30, 12:30, 1:30, 2:30 that's 5 hours and from 2:30 to 2:45 is 15 minutes.
Hope this helps. :)