\begin{tabular}{|c|c|c|}
\hline \begin{tabular}{c}
proposed \\
addition or subtraction
\end{tabular} & \begin{tabular}{c}
Is this \\
possible?
\end{tabular} & result \\
\hline $27.000 \mathrm{~m}+42.000 \mathrm{~mm}=?$ & \begin{tabular}{l}
yes \\
0 no
\end{tabular} & $\square$ \\
\hline $37.0 \mathrm{~km}-16.0 \mathrm{~km}=?$ & \begin{tabular}{c}
yes \\
0 no
\end{tabular} & $\square$ \\
\hline $40.000 \mathrm{~kg}+43.000 \mathrm{~m}=?$ & \begin{tabular}{l}
yes \\
no
\end{tabular} \\
\hline
\end{tabular}

Step 1 ：Convert 27.000 m to millimeters: \(27.000 \mathrm{~m} = 27000.000 \mathrm{~mm}\)

Step 2 ：Add the two measurements: \(27000.000 \mathrm{~mm} + 42.000 \mathrm{~mm} = 27042.000 \mathrm{~mm}\)

Step 3 ：\(\boxed{27042.000 \mathrm{~mm}}\) or \(\boxed{27.042 \mathrm{~m}}\) is the result of the first operation

Step 4 ：Subtract the two measurements: \(37.0 \mathrm{~km} - 16.0 \mathrm{~km} = 21.0 \mathrm{~km}\)

Step 5 ：\(\boxed{21.0 \mathrm{~km}}\) is the result of the second operation

Step 6 ：The third operation is not possible because the units are different and cannot be converted to each other. The units of kilograms and meters measure different quantities (mass and length, respectively), so they cannot be added together.