Method 1:
[tex]\dfrac{a}{20}+\dfrac{14}{15}=\dfrac{9}{15}\ \ \ \ |multiply\ both\ sides\ by\ 60\\\\60\cdot\dfrac{a}{20}+60\cdot\dfrac{14}{15}=60\cdot\dfrac{9}{15}\\\\3a+4\cdot14=4\cdot9\\\\3a+56=36\ \ \ \ |subtract\ 56\ from\ both\ sides\\\\3a=-20\ \ \ \ |divide\ both\ sides\ by\ 3\\\\\boxed{a=-\frac{20}{3}\to a=-6\frac{2}{3}}[/tex]
Method 2.
[tex]\dfrac{a}{20}+\dfrac{14}{15}=\dfrac{9}{15}\ \ \ \ |subtract\ \dfrac{14}{15}\ form\ both\ sides\\\\\dfrac{a}{20}=-\dfrac{5}{15}\\\\\dfrac{a}{20}=-\dfrac{1}{3}\ \ \ \ |multiply\ both\ sides\ by\ 20\\\\\boxed{a=-\dfrac{20}{3}\to a=-6\frac{2}{3}}[/tex]
