Word problem

Question

Bryan goes to school everyday at 6:00am. he leaves school 7 hours and 15 minutes later. if Bryan were to go to school at 6:15, how long would he be in school? And what time would he get out?

Answer 1

If Bryan goes in a 6am, and leaves 7 hours and 15 minutes later, that means that he leaves at 1:15 pm exactly. 
So now if he needs to stay in school 7 hours and 15 minutes no matter what, we just shift that amount of time over, from 6 am to 6:15 am as a start point. So 6:15 am, spring forward 7 hours, its 1:15 pm, then another 15 minutes, and we come to 1:30 pm. 
However, if the amount of time he spends in school isn't the constant (constant meaning it doesn't change), then in order to get out at the original end time (1:15 pm) after going in at 6:15 am, he would be in school for only 7 hours.
Hope this answers your question!