Final answer:
option A.The parachutist's rate of descent in feet per second is converted to miles per hour using the conversion factors of feet to miles and seconds to hours, resulting in 12.27 mph.
Step-by-step explanation:
The question involves converting a speed from feet per second to miles per hour. The parachutist's rate of descent in feet per second needs to be converted using the relationship between feet and miles, and seconds and hours. To find the rate in miles per hour (mph), use the conversion factors: 1 mile = 5280 feet, and 1 hour = 3600 seconds.
First convert the descent rate to feet per hour by multiplying 18 feet per second by 3600 seconds:
18 feet/second * 3600 seconds/hour = 64800 feet/hour
Next, convert feet to miles:
64800 feet/hour / 5280 feet/mile = 12.27 mph
Thus, the parachutist's rate of descent is 12.27 mph, which corresponds to answer option A.