An algebra problem!
But seriously, if you have two variables, you need two equations to solve it.
From what you've provided, you can put x in terms of y:
or you can put y in terms of x (I'll let you do that one), but you can't solve it without a second equation. By itself, this equation has an infinite number of solutions. For instance, if y=2, x=-7 2/3; if y=-2, y=12 1/3; if y=10,000,000, x=-49,999,997 2/3 (try plugging those pairs in and see).
The way to visualize it is to graph the equation--in this case, it's a straight line. If you had another equation, it would be a different line. The solution would be represented by where the lines cross.