As some of colleagues have mentioned, you can solve this task by looking at those equations like equations of lines, which they are actually. You would write them as: \(\displaystyle y=-ax-5 \) and \(\displaystyle y=-\dfrac{1}{6}x+\dfrac{1}{2} \). This system won't have any solution when those two lines are parallel( they do not intersect). Two lines that are parallel have something equal.... you can use that fact. You just have to set the equation from what I've told you and you will be able to get a value of 'a'.