\[\boxed{\text{6.42.}}\]
\[\textbf{а)}\ 5,42 < z < 9,76\ \ \ \]
\[z = 6;\ 8.\ \]
\[\textbf{б)}\ 0,3 < z < 0,4\text{\ \ }\ \]
\[z = 0,34;\ \ 0,37.\ \]
\[\textbf{в)}\ 3,6 < z < 3,7\ \ \]
\[z = 3,61;\ \ 3,69.\ \]
\[\textbf{г)}\ 14,99 < z < 15\text{\ \ }\ \]
\[z = 14,9901;\ \ 14,991.\ \]
\[\textbf{д)}\ 8 < z < 8,01\text{\ \ \ \ \ \ \ }\]
\[z = 8,0001;\ \ 8,001.\ \]
\[\textbf{е)}\ 1,123 < z < 1,124\ \ \]
\[z = 1,12301;\ \ 1,1237.\ \ \]