A runner moves at a constant speed of 15 miles per hour. What is this speed in feet per second? (1 mile = 5,280 feet)

Convert miles to feet and hours to seconds. $15 \frac{\text{mi}}{\text{hr}} \times \frac{5280 \text{ ft}}{1 \text{ mi}} \times \frac{1 \text{ hr}}{3600 \text{ s}} = \frac{79{,}200}{3{,}600} = 22$ feet per second, choice B. A quick check: 60 mph is exactly 88 ft/s, and $\frac{15}{60} \times 88 = 22$. Choice A (15) leaves the number unchanged. Choice C (88) is the speed for 60 mph, not 15. Choice D (4.4) does not come from a correct conversion; it would be the speed for 3 mph. Write out the unit conversion so that the units cancel.