9. (5 points) A certain project, initially 6 people spent 35 days to complete $\frac{1}{3}$ of the entire project, after that, 6 more people joined to complete this project together. Then, the total time to complete this project is $\qquad$ days.
9. (5 points) A certain project, initially worked on by 6 people for 35 days to complete $\frac{1}{3}$ of the entire project, then 6 more people were added to complete the project. The total time to complete the project is $\qquad$ days.

【Solution】Solution: Consider the total workload as unit “1”. The remaining workload is $1-\frac{1}{3}=\frac{2}{3}$, and the work efficiency of one person is $\frac{1}{3}$ $\div 6 \div 35$,
$$
\begin{array}{l}
\left(1-\frac{1}{3}\right) \div\left[\frac{1}{3} \div 6 \div 35 \times(6+6)\right] \\
= \frac{2}{3} \div\left(\frac{1}{3} \div 6 \div 35 \times 12\right) \\
= \frac{2}{3} \div \frac{2}{105} \\
= 35 \text { (days) } \\
35+35=70 \text { (days) }
\end{array}
$$

Answer: The total time to complete the project is 70 days.
Therefore, the answer is: 70.