Three customers are at the hairdresser, each paying their bill at the cash register.

- The first customer pays an amount equal to the amount in the cash register and receives 10 reais in change.
- The second customer performs the same operation as the first.
- The third customer performs the same operation as the first.

Find the initial amount in the cash register, knowing that, at the end of the three operations, the cash register was empty.
Let $x$ be the initial amount in the cash register. This amount plus what the three customers paid will result in an empty cash register.

- The first customer pays $x-10$ and, after him, there are $x+x-10=2 x-10$ reais in the cash register.
- The second customer pays $(2 x-10)-10=2 x-20$ and, after him, there are $(2 x-10)+(2 x-20)=4 x-30$ in the cash register.
- The third customer pays $(4 x-30)-10=4 x-40$ and, after him, there are $(4 x-30)+(4 x-40)=8 x-70$ in the cash register.

Since the cash register is empty after the third customer, $8 x-70=0$, that is,

$$
x=70 / 8=8.75 \text { reais. }
$$