12am to 3pm is how many hours

15
that's why in 24 hours clock it is 15:00

15+24d, where A is the day on which your 12am occurs, B is the day on which your 3pm occurs, and h is the number of days from A to B. :)

15 hours - 3p.m. = 15:00 hrs in the 24 hour clock!
or u can even count - 12 am. to 12 pm. makes 12 hours and 12 pm to 3pm makes 3 hours . So 12 + 3 = 15 hours
Hope i helped! :D

its exactly 15 hours :)

12 am -> 0000 hr
3 pm -> 1500 hr

hence, 1500 - 0000 = 15 hrs :)