6.5 goes in the first box and 5.5 goes in the second box.
Explanation for first box: 13+2 is 15 and half of 15 is 7.5 so you need to take 13 and subtract 7.5. Once you do that, you end up with 6.5
Explanation for second box: (The negative 7 doesn't matter because you want the absolute value) 18+7 is 25 and half of 25 is 12.5. 18-12.5 is 5.5 so the answer would be 5.5