Hello, you have y as a function of m and x as a function of m, to get y as a function of x, you need to express m as a function of x.
[tex]x=3m-4<=>x+4=3m<=>m=\dfrac{x+4}{3} \\ \\y=6-m=6-\dfrac{x+4}{3}=\dfrac{18-x-4}{3}=\boxed{\dfrac{14-x}{3}}[/tex]
Voila !
