[tex]\dfrac{5}{6}$ din $ a + \dfrac{1}{3}$ din $ a = 42 \Leftrightarrow \dfrac{5}{6}\cdot a + \dfrac{1}{3}\cdot a = 42 \Big|\cdot 6\\ \\ \Rightarrow\dfrac{6\cdot 5}{6}\cdot a + \dfrac{6\cdot 1}{3}\cdot a = 6\cdot 42 \Rightarrow 5\cdot a+2\cdot a = 252 \Rightarrow 7\cdot a = 252 \Rightarrow \\ \\ \Rightarrow a = \dfrac{252}{7} \Rightarrow\boxed{a =36}[/tex]
