\[\boxed{\text{6.141.}}\]
\[1)\ KP = MN + 2,53 =\]
\[= 5,3 + 2,53 = 7,83\ (дм)\text{.\ }\]
\[2)\ NK = KP + 1,73 =\]
\[= 7,83 + 1,73 = 9,56\ (дм)\text{.\ }\]
\[3)\ PD = MD - 1,9 = 5,3 - 1,9 =\]
\[= 3,4\ (дм)\text{.\ }\]
\[4)\ P_{\text{MNKPD}} =\]
\[= 5,3 + 5,3 + 7,83 + 9,56 + 3,4 =\]
\[= 10,6 + 17,39 + 3,4 =\]
\[= 27,99 + 3,4 = 31,39\ (дм)\text{.\ }\]
\[\textbf{а)}\ 31,39\ дм \approx 31,4\ дм;\ \]
\[\textbf{б)}\ 31,39\ дм \approx 31\ дм;\ \]
\[\textbf{в)}\ 31,39\ дм = 313,9\ см \approx\]
\[\approx 314\ см;\ \]
\[\textbf{г)}\ 31,39\ дм = 3,139\ м \approx 3,1\ м.\ \]
\[Ответ:31,39\ дм.\ \ \ \]