12. The figure below shows the number of days required for three individuals, A, B, and C, to complete a certain project individually. According to the information in the figure, if A works for 2 days first, followed by B and C working together for 4 days, and the remaining work is completed by C alone, then the total number of days to complete the project is.
12. The figure shows the number of days required for three individuals, A, B, and C, to complete a certain project individually. According to the information in the figure, if A works for 2 days first, then B and C work together for 4 days, and finally, the remaining work is completed by C alone, the total time to complete the project is 9 $\qquad$ days.
【Solution】Solution: According to the problem, we know:

The work efficiencies of A, B, and C are: $\frac{1}{10}, \frac{1}{12}, \frac{1}{15}$;
The total work done by A and B is: $\frac{1}{10} \times 2+\left(\frac{1}{12}+\frac{1}{15}\right) \times 4=\frac{4}{5}$;
The number of days C works is: $\left(1-\frac{4}{5}\right) \div \frac{1}{15}=3$ (days);
The total work time is $2+4+3=9$
Therefore, the answer is: 9