\[\frac{a + 2b}{3} - \frac{2a - 5b}{6} =\]
\[= \frac{1}{6} \cdot \left( 2 \cdot (a + 2b) - (2a - 5b) \right) =\]
\[= \frac{1}{6} \cdot (2a + 4b - 2a + 5b) =\]
\[= \frac{1}{6} \cdot 9b = \frac{9}{6}b = \frac{3}{2}\text{b.}\]
\[a = 2,8;\ \ \ b = 0:\]
\[\frac{3}{2}b = \frac{3}{2} \cdot 0 = 0.\]