Final answer:
To convert a speed of 20 m/s to km/h, multiply by 3.6, giving a result of 72 km/h. Therefore, the correct answer is 72 km/h.
Step-by-step explanation:
To convert the stuntman's driving speed from meters per second (m/s) to kilometers per hour (km/h), we use the ratio that 1 m/s is equivalent to 3.6 km/h. Thus, to get the speed in km/h, we multiply the speed in m/s by 3.6. The calculation for the given speed of 20 m/s is as follows:
Speed in km/h = Speed in m/s × 3.6
Speed in km/h = 20 m/s × 3.6 km/h
Speed in km/h = 72 km/h
Therefore, the correct answer is (b) 72 km/h.