What is the answer to the mission 7 in 39 clues?

box 1.

8 1 6

3 5 7

4 9 2

sum: 15

box 2.

1 15 14 4

12 6 7 9

8 10 11 5

13 3 2 16

magic sum: 34

box 3.

3 17 16 6

14 8 9 11

10 12 13 7

15 5 4 18

magic sum: 42