Carson is going to spend 4 hours at a carnival. The wait for the roller coaster is 30 minutes, the wait for the tilt-a-whirl is 60 minutes, and the wait for the giant slide is 15 minutes. If Carson rides the roller coaster 4 times and the tilt-a-whirl once, how many times can he ride the giant slide? (Wait times include the time actually spent on the ride.)
Please reason step by step, and put your final answer within \boxed{}.
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