Gage skated 1 hr 15 min each day for 5 days and 1 hr 30 min each day for 3 days.  How many minutes would he have to skate the ninth day in order to average 85 minutes of skating each day for the entire time?
So if 1 hour 15 minutes is 75 minutes, then he skated 75 minutes each day for 5 days, that's 375 minutes. And if 1 hour 30 minutes is 90 minutes, then he skated 90 minutes each day for 3 days, that's 270 minutes. So far he has skated 375 + 270 minutes = 645 minutes. And to average 85 minutes each day for 9 days, he would have to skate 85 minutes each day * 9 days = 765 minutes. So on the ninth day he would have to skate 765 total minutes - 645 minutes already spent = 120 minutes. Yep.

