Answer:
31
the difference between the numbers is the number, plus 2, so for example, the difference between 7 and 10 is 3, add two and you have 5, and ten plus 5 equals 15. Using this formula, we have 5+2=7, which is 15+7=22. For the missing number, we have 7 (the last number used) +2=9, so, 22+9=31.
Explanation:
im kinda bad at explaining things, but i really hoped this helped :)