13.186. A brigade of masons took on the task of laying $432 \mathrm{~m}^{3}$ of masonry, but in reality, 4 fewer people showed up for work. How many masons are there in the brigade if it is known that each working mason had to lay $9 \mathrm{~m}^{3}$ more than initially planned?
## Solution.

Let there be $x$ masons in the team. Each mason lays $\frac{432}{x}$ m $^{3}$ of masonry. Since $x-4$ masons were working, each had to lay $\frac{432}{x}+9$ m $^{3}$ of masonry. Therefore, $\left(\frac{432}{x}+9\right)(x-4)=432$, from which $x=16$.

## Answer: 16.