Is this separable? I'm trying, but I'm not sure if I'm on the right track:
y' = (x+y)/(x+2y)
dy/dx = (x+y)/(x+2y)
multiply both sides by dx:
dy = (x+y)/(x+2y) dx
Now I am not sure what to do because if I get (x+2y) to the other side, it'd still have an x and would be attached to the dy as well.