\[3x - 9y = 1 \Longrightarrow x - 3y = \frac{1}{3}\]
\[\frac{x^{2} - 9y^{2}}{1,5x + 1,5y} =\]
\[= \frac{(x - 3y)(x + 3y)}{1,5 \cdot (x + 3y)} = \frac{\frac{1}{3}}{1,5} =\]
\[= \frac{1}{4,5} = \frac{10}{45} = \frac{2}{9}\]