Answer:
4. 3
Explanation:
If you multiply 2 by 3 it'll equal to 6. Same with 7 x 3= 21.
You could also subtract 7 from 2 equalling 5 and 21 - 6 equal to 15. Then you would but y over x giving you 15/5. 15 divided by 5 is 3. So both ways you get 3.
Hope that helps :)