The person above me got that horrible wrong, do not put that.
You also wrote the question wrong, please be more careful when posting.
x-3y=18
Move x to the other side by subtracting it since it’s positive.
-3y = -x + 18
Divide the whole equation by -3 to find the value of just 1 y.
-3y/-3 = -x/-3 + 18/-3
y = 1/3x -6