13.174. In four boxes, there is tea. When 9 kg were taken out of each box, the total that remained in all of them together was as much as there was in each one. How much tea was in each box?
## Solution.

Let there be $x$ kg of tea in each box, leaving $(x-9)$ kg. According to the condition, $4(x-9)=x$, from which $x=12$ kg.

Answer: $12 \mathrm{kg}$.