Do you mean 90,000?
If so, then move the decimal 4 places to the left to make the number land between 1-10. Then use the number of places as the power of 10. If you are moving the decimal right, then the power will be negative.
9x10^4 is 90,000 in scientific notation.
9x10^-4 is 0.0009 in scientific notation.
