\[\left( \frac{1}{3}x + y \right) - \frac{2}{3}(x + 1,5y) =\]
\[= \frac{1}{3}x + y - \frac{2}{3}\left( x + \frac{3}{2}y \right) =\]
\[= \frac{1}{3}x + y - \frac{2}{3}x - y = - \frac{1}{3}\text{x.}\]