The correct option is
C 5
Here the sum of top two numbers divided by the difference between two numbers at the bottom gives the number at right.
(7+5)÷(9−6)=4
(9+7)÷(6−4)=8
Therefore,
(12+13)÷(10−x)=5
i.e. (25 ÷ 5 = 10-x )
So, ? has to be replaced by 5 (option C)