Practical question on natural logs

I refer to reading 10, end of reading question 3 and 4, CFAI Level 2 books. In question 3, material refers to natural log of 100 million and 1 billion USD. In solution to question 3, they take natural log of 100 and 1000 (or scale it to millions - ln 100, ln 1000) In question 4, material refers to natural log of 900,000 USD. In solution to question 4, they take natural log of 900,000 (they don’t scale it - ln 900,000). It looks like that I am missing something here. It’s obviously important what number you put in the calculation of natural log. How do I know when to scale (or not) when I am taking natural logs of real values? Thank you!

i think they tell you in the question 3 that the variable is in millions of usd

You are right, they specify the scale! Thank you very much!