Question: how many hours is 11am to 3pm?
Answer: So 11:00 am is 1 hour before noon, and 3:00 pm is 3 hours after noon, making 4 hours in all between them. It is much better and leads to less confusion to use a 24 hour clock, where 11:00 am is 11:00 and 3:00 pm is 15:00, making the difference of 4 hours much more obvious.