Hey there! So what you want to do is plug y into the equation. So thats 3x-2x=10
You got it from here? Or do you need more help?
FOR X: write 3x-y=10 in terms of y, add -3x from both sides, and divide both sides by -1 to simplify it down to y=3x-10. then, write 3x-10 in terms of y, add -3x to both sides, and divide both sides by -1 to get x=10
FOR Y: substitute 10 in terms of y and simplify to get x=20