\[\boxed{\text{6.138.}}\]
\[\textbf{а)}\ 3,791 \approx 3,8;\ \]
\[5,2626 \approx 5,3;\ \]
\[311,954 \approx 312,0;\ \]
\[40,57 \approx 40,6.\ \]
\[\textbf{б)}\ 0,08324 \approx 0,08;\ \]
\[3,46511 \approx 3,47;\ \]
\[20,097 \approx 20,10;\ \]
\[87,423 \approx 87,42;\ \]
\[9,655 \approx 9,66.\ \]
\[\textbf{в)}\ 238,2 \approx 240;\ \]
\[4\ 175,02 \approx 4\ 180;\ \]
\[333,3 \approx 330;\ \]
\[500,9 \approx 500;\ \]
\[248 \approx 250.\ \ \ \]