3/4 is 45 minutes, cause a quarter of an hour is 15 minutes. 6-9 = -3 so you basically do Noon subtracted by another 3 hours which is 9 am, then subtract those 45 minutes
6pm - 6 hours = 12pm
(Noon) 12pm - 3 hours= 9am
then 45 minutes
9am - 45 minutes
8:15AM