Puzzles - Number puzzles

7.
Answer
:
6
Explanation
:
The numbers in each row and column add up to 15.

8.
Answer
:
40
Explanation
:
Moving from left to right, numbers increase by 2,3,4 and 5.

9.
Answer
:
9
Explanation
:
In each square of the diagram, the sum of the numbers is always 22.