0.0001 is a very small number, so we will use the scientific notation to help us answer this. When using the scientific notation with very small numbers, we will multiply this number by 10. When we multiply a decimal, we "move" the decimal place to the right. The scientific notation states we will multiply until we get a number greater or equal to one, but less then 10. Our process will look something like this.
0.0001 -> 0.001 -> 0.01 -> 0.1 -> 1
We now have a number greater or equal to 1 but less then 10- which is 1!
Now, we have to find our exponent. How many times did we multiply by 10?
We multiplied 4 times. So now we have 10^4. But we are not done. For very small numbers, the exponent is negative, so our exponent is negative, In which leaves us with the answer of 10^-4.
With best wishes- Asia Gil <3