We know that Carson takes twice as long as Jerry to get to the school, so we can find the time it takes him by multiplying Jerry's time by 2: 15 minutes * 2 = <<15*2=30>>30 minutes
Then convert that time to house by dividing by 60 minutes/hour = 30 minutes / 60 minutes/hour = <<30/60=.5>>.5 hour
Then divide the distance Carson runs by the time it takes him to run it to find his speed: 4 miles / 0.5 hours = <<4/0.5=8>>8 miles/hour
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