The correct option is A 15 hours
In 12 hours format, the duration between 3:00 am to 3:00 pm is equal to 12 hours.
and that between 3:00 pm and 6:00 pm is:
h :min6 :00−3 :00––––––––––––3 :00 =3 hours
So, the total duration between 3:00 am and 6:00 pm is
12 + 3 = 15 hours.