$\begin{array}{l} a)\dfrac{5}{3} = \dfrac{{5a}}{{3a}}\,\,\,\,\,\,\,\,\,\,\,\,\dfrac{{5a - 6}}{{3a}}\\ b)\dfrac{{2x}}{3} = \dfrac{{2ax}}{{3a}}\,\,\,\,\,\,\,\,\,\,\,\,\,\dfrac{{2ax + 3x}}{{3a}}\\ c)\dfrac{b}{{6a}} = \dfrac{{b.3b}}{{18ab}} = \dfrac{{3{b^2}}}{{18ab}}\,\,\,\,\,\,\dfrac{{4a + 3{b^2}}}{{18ab}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\dfrac{x}{{9b}} = \dfrac{{x.2a}}{{18ab}} = \dfrac{{2ax}}{{18ab}} \end{array}$