Answer: Formula for average speed is distance/time
so your answer would be 20/4 so it would be 5 mph (miles per hour)
Step-by-step explanation:
The formula you use to find average speed (meaning "how fast") is distance over time, the distance is 20 miles, and the time that was used to travel this distance was 4 hours
so you would do 20/4 which is equal to 5 miles per hour.
Hope I helped! :)