\[\boxed{\text{6.147.}}\]
\[\textbf{а)}\ 5,6 < x < 5,7\ \ \ \ \ \]
\[x = 5,63;\ 5,67.\ \]
\[\textbf{б)}\ 0,2 < x < 0,3\ \ \ \]
\[x = 0,201;\ 0,239.\ \]
\[\textbf{в)}\ 0 < x < 0,002\ \ \ \ \ \ \ \]
\[x = 0,0001;\ 0,00018.\ \]
\[\textbf{г)}\ 5,2 < x < 5,21\ \ \ \ \ \]
\[x = 5,2003;\ 5,2008.\text{\ \ \ }\]