I hope I got it
basically its sequence with addition pattern
in 2nd row
1
7 == 1st term + 6
2 == second term -5
-5 == 1st term
n == 6+ first term hence 1
-4 == 1-5 = -4
gives n = 1
in 3rd col
m == first term
10 ==6+first term hence m = 4
5 == second term - 5 = 5
hence m + n = 4 + 1 = 5
Wounded by GMAT but not dead