Parts $P1 – P7$ are machined first on a milling machine and then polished at a separate machine. Using the information in the following table, the minimum total completion time required tor carrying out both the operations for all $7$ parts is _____________ hours.

$$\begin{array}{|c|c|} \hline \text{Part} & \text{Milling (hours)} & \text{Polishing (hours)} \\ \hline\text{P 1} & 8 & 6 \\ \hline \text{P 2} & 3 & 2 \\ \hline\text{P 3} & 3 & 4 \\ \hline \text{P 4} & 4 & 6 \\ \hline \text{P 5} & 5 & 7 \\ \hline \text{P 6} & 6 & 4 \\ \hline \text{P 7} & 2 & 1 \\ \hline \end{array}$$

1. $31$
2. $33$
3. $30$
4. $32$