Is 6 the factor of positive integer x ?

St1: x = 7k + 5 = 5, 12, 19, ..........
If x = 5 then 6 is not a factor of x
If x = 12 then 6 is a factor of x
Not sufficient

St2: x = 9k + 3 = 3, 12, 21, ...........
If x = 3 then 6 is not a factor of x
If x = 12 then 6 is a factor of x

Combining St1 and St2,
x = 12 then 6 is a factor of x.
But do all the integers follow this trend? No.
x = 7(10) + 5 = 9(8) + 3 = 75
6 is not a factor of 75.
Not sufficient

Answer: E

P.S: You may ask how I found out the intersections. When the multiples are different just find the first point of intersection and increase the LHS multiple by the common multiple of RHS and viceversa (Sorry if my explanation was not clear but the example below should help you understand)
7(1) + 5 = 9(1) + 3
7(10) + 5 = 9(8) + 3
7(19) + 5 = 9(15) + 3

We can see that the multiple on LHS is increasing in steps of 9 and multiple on RHS is increasing in steps of 7.

If, 10k + 2 = 12k + 4
First point of intersection = 10(5) + 2 = 12(4) + 2
Later increase the multiples of both the sides: 10(17) + 2 = 12(14) + 2