Answer:
6
Explanation:
Range: The difference between the lowest and highest values. In {4, 6, 9, 3, 7} the lowest value is 3, and the highest is 9, so the range is 9 − 3 = 6.
So the difference between 15 (being the lowest value) and 21 (being the highest value) is 6.
Don't let the visual confuse you :)