michael walks at a rate of 6 feet per second.which is the closest to this rate in mph?
1 mile=5280 feet
1 hour=3600 seconds.
Your two selections are not speeds. They are conversion factors.
The speed in mph is 15/22 * 6 = 4.09 mph
You can derive the 15/22 factor from the 5280 ft/mile and 3600 sec/hr, but the rule that 15 mph = 22 ft/s, exactly, is worth memorizing