Answer :
Given,
The age of the solar system is 4.5 billion years.
One billion is 1,000,000,000.
In scientific notation, we can write one billion as 1×10⁹.
Therefore to express any number in billions we need to multiply it with the above number.
Therefore, we can write 4.5 billion years as,
[tex]4.5\times1\times10^9=4.5\times10^9\text{ years}[/tex]Therefore we can express 4.5 billion years as 4.5