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.