You can put this solution on YOUR website! At 5 miles a hour speed, how long does it take to go 48 feet?
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15 mi/hr = 22 ft/sec (take my word for it, or confirm it)
--> 5 mi/hr = 22/3 ft/sec
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d = r*t
t = d/r, d = 48 ft, r = 22/3 ft/sec