Answer:
The correct answer is: 10-20-30
Step-by-step explanation:
13 is between 10 and 20. The closest 10 for 13 is 10, because it's only 3 away (13 the other option would be 20 but it's 7 away, so way more.)
21 is between 20 and 30. The closest 10 for 21 is 20 ( it's only 1 away from 20, the other option would be 30 but it's 9 away, so way more.)
29 is between 20 and 30. The closest 10 for 29 is 30 (it's only 1 away from 30, the other option would be 20 but it's 9 away, so way more.)