Well, first of all, we can simplify the bottom equation:

6a + 2b = k + 3a + mb

into

3a + 2b = k + mb

Because the top equation is also 3a+2b, and the bottom is also 3a+2b, and there are infinitely many solutions, that means:

k+mb = 2

And because b can be anything, that means m has to be 0 to work. that means k = 2

k = 2

m = 0