7, 1,2,5,4,6,9,8, 15, 13(),2 1

7, 1, 2, 5

4, 6, 9, 8

15, 13,(),2 1

In this way, the first two numbers of each vertical row are added, and the second number is the third number, that is, 7+4+4= 15, 1+6 = 13, 2+9+9=20, 5+8+8 = 2/kloc-0.

So it's 20 in brackets.