\[\boxed{\text{5.347.}}\]
\[\textbf{а)}\ \frac{5}{9} = \frac{n}{27}\]
\[\frac{15}{27} = \frac{n}{27}\]
\[n = 15.\ \]
\[Ответ:n = 15.\]
\[\textbf{б)}\ \frac{1}{3} = \frac{7}{c}\]
\[\frac{7}{21} = \frac{7}{c}\]
\[c = 21\text{.\ }\]
\[Ответ:c = 21.\ \]
\[\textbf{в)}\ \frac{r}{5} = \frac{5}{z}\]
\[r = 5;\ \ z = 5\text{.\ }\]
\[Ответ:r = 5;\ \ z = 5\text{.\ }\]
\[\textbf{г)}\ \frac{m}{12} = \frac{5}{c}\]
\[m = 5;\ \ c = 12.\ \]
\[Ответ:m = 5;\ \ c = 12\text{.\ \ }\]