Answer :

iGreen
2/3 = x/(3x + y)

Cross multiply:

3x = 2(3x + y)

Distribute 2:

3x = 6x + 2y

Subtract 6x to both sides:

-3x = 2y

Divide 'y' to both sides:

-3x/y = 2

Divide -3 to both sides:

x/y = -2/3
2/3 = x/3x + y
2(3x + y) = 3x
2(3x) + 2(y) = 3x
    6x + 2y = 3x
 - 6x           - 6x
           2y = -3x
            2       2
             y = -1.5x