First figure out how many minutes Carson spends at the carnival by multiplying the number of hours he's there by the number of minutes per hour: 4 hours * 60 minutes/hour = <<4*60=240>>240 minutes
Then figure out how long Carson spends waiting for the roller coaster by multiplying the wait time per ride by the number of rides: 4 rides * 30 minutes/ride = <<4*30=120>>120 minutes
Now subtract the time Carson spends on the roller coaster and tilt-a-whirl from the total time he spends at the park to find out how much time he has left: 240 minutes - 120 minutes - 60 minutes = <<240-120-60=60>>60 minutes
Now divide the time Carson has left by the wait time for the giant slide to see how many times he can ride it: 60 minutes / 15 minutes/ride = <<60/15=4>>4 rides
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