[tex] \dfrac{3b^2}{4a^2}+\dfrac{5b}{3a}-\dfrac{1}{6a^3}=\dfrac{3b^2\cdot3a}{4a^2\cdot3a}+\dfrac{5b\cdot4a^2}{3a\cdot4a^2}-\dfrac{1\cdot2}{6a^3\cdot2}\\\\=\dfrac{9ab^2}{12a^3}+\dfrac{20a^2b}{12a^3}-\dfrac{2}{12a^3}=\boxed{\dfrac{20a^2b-2+9ab^2}{12a^3}} [/tex]
