Let me translate it in math term:
6 and five sixth of an hour plus 103 minutes means: 6*(5/6)*1hour +103 mins = 6*(5/6)*60mins +103mins = 300mins +103 mins = 403 mins
Convert 403 mins in hours and mins
6 hours = 360 mins
403 - 360 = 43mins
so 403mins = 6 hours 43 minutes