\[\boxed{\text{5.\ 73}}\]
\[\textbf{а)} - 5m \rightarrow k = - 5\]
\[\textbf{б)}\ \frac{4}{7}\text{mn} \rightarrow k = \frac{4}{7}\]
\[\textbf{в)}\ ab \rightarrow k = 1\]
\[\textbf{г)} - cd \rightarrow k = - 1\]
\[\textbf{д)} - a \cdot ( - c) = ac \rightarrow k = 1\]
\[\textbf{е)} - \frac{4}{7}a \cdot \frac{7}{8}b = - \frac{1}{2}\text{ab} \rightarrow k =\]
\[= - \frac{1}{2}\]
\[\textbf{ж)}\ 0,25b \cdot 4a = ab \rightarrow k = 1\]
\[\textbf{з)} - 4x \cdot ( - 0,3y) =\]
\[= 1,2xy \rightarrow k = 1,2\]