Per Slate (and it’s worth quoting this entirely):
Here’s how the Alliance does the math:
First, they note that $100 million amounted to about 0.7 percent of Google’s total revenue in 2008. They then assume, without much evidence,1 that it is responsible for an equal share of the company’s revenue today.
Second, they attempt to estimate how much revenue Google gets from news-related searches on its main site. They do so by multiplying 0.7, a number they functionally pulled from nowhere, by six. Why six? Because publishers say they get six times more traffic referrals from normal Google searches than from the news app. This leads them to conclude that people typing “Mueller report” and such into the Google search bar is worth 4.2 percent of the company’s revenue.
Third, they do some addition: 4.2% + 0.7% = 4.9%. Multiply that by $96 billion in revenue, and you get a grand total $4.7 billion.