\[\frac{2a + b}{3a - 4b};\ \ если\ a = - 6;\ \ b = 3.\]
\[\frac{2a + b}{3a - 4b} = \frac{2 \cdot ( - 6) + 3}{3 \cdot ( - 6) - 4 \cdot 3} =\]
\[= \frac{- 12 + 3}{- 18 - 12} = \frac{- 9}{- 30} = \frac{9}{30} =\]
\[= \frac{3}{10} = 0,3.\]