1
Input: 4 → [?] → 20, what is the rule? =
2
Input: 9 → [?] → 19, what is the rule? =
3
Input: 7 → [?] → 12, what is the rule? =
4
Input: 10 → [?] → 30, what is the rule? =
6
Input: 2 → [?] → 4, what is the rule? =
7
Input: 3 → [?] → 15, what is the rule? =