It would be 6 miles per hour.
mph is a unit for speed. And the formula for speed is s=distance /time
So the distance is 2 miles
And the time is 20 minutes
*for this question you need to convert the minutes to hours to get the right units
20mins =0.3 hours (approx) [20/60 to get it in hours]
2 miles/0.3 hours ≈ 6 mph