Okie, to solve this, lets just plug in the values into the final formulas. I tried doing it the actual way and it had failed lol but this works too. So to see which equation is correct, all we need to do ( i know because I tried already ) is find the equation that passes through the actual point. This means both sides of the equation should be equal when the variables are plugged in.
3(12) + 2(-6) = 26? nope 24 = 26
3(12) + 2(-6) = 6? nope 24 = 6
2 (12) - 3(-6) = 42? yup 42 = 42
2(12) - 3(-6) =-48? nope 42 = -48
So in doing this, we can see that only one of the equations pass through the point (12,-6) and therefore C. is the answer
I hope this helps :-)