Kerri's answer is set up correctly, just wanted to include units. The math shown is just a conversion from one unit to another. She first set up the rate (ft/sec), then converted sec to hours (3600 sec in one hour), followed by converting feet to miles (5290 ft in one mile). The final answer has a unit in mi/hr. The basic rule is that if the problem has units (words), then the answer needs units (words) in it.