What is this formula?

Question

Mathematics

Tell me there is a number, we take 10% then again 10% and so on up to 0 we get values ​​whose sum is, for example, 100.
X + 10%x + 10%(10%x) + ... = 100
We need to get the initial value .

Tried the progression, but I don't have the number of steps. Only a step of 10% and a sum of 100 need to find the original number.
What formula can be used?