\[\frac{a + 2b}{b} = 7 \Longrightarrow a + 2b =\]
\[= 7b \Longrightarrow a = 5b\]
\[\frac{3a + 4b}{a} = \frac{15b + 4b}{5b} = \frac{19b}{5b} =\]
\[= \frac{19}{5} = 3,8\]