Answer:
What you want to do is solve for m in whichever equation it's easier to so in, then substitute that in to the other equation. For instance:
X=3m-4
Y=6-m
Solve the 2nd equation to get m=6-y
Plug that into the first equation to get x=3(6-y)-4
X=18-3y-4
X-14=-3y
14-x=3y
Y=(14-x)/3