HELP SOLVE MY 8-YR-OLD NEPHEW'S MATH PROBLEM

Please share your answer and why.
  1. What is A?
  2. Appropriate age for such question? 😳
  3. 2
    The bottom row adds up to 24 as well as the middle column so the top row, I figure: 2 + 10 + 12= 24.
    Suggested by   @eclecticmouse