I'm not really sure how I would write it down to show how I worked it out.
For me, I usually know in scientific notation, it's usually a decimal number multipled by 10 raised to a certain level of power.
So I just did 4,600,000,000 and turned that into a decimal without its extra zeros, which would be 4.6. Then I worked out how many places the decimal would be from there, which is 9 spaces behind 4.6.
For example the age of the Earth (see above) can be written as 4.6 X 109 years. This means that this number has 9 places after the decimal place - filled with zeros unless a number comes after the decimal when writing scientific notation. So 4.6 X 109 years represents 4600000000 years.
