\(\begin{array}{c|c}
\text{Unit of output} & \text{Table cost}\\
\hline
1 & 20 \\
2 & 32 \\
3 & 42 \\
4 & 48 \\
5 & 50 \\
\end{array}\)
in the above table, the marginal cost of the 3rd unit of output is