Probability Help

Hello! Taking an introductory course on statistics in college. Confused about one question. It reads:
The IRS reports that 15% of the tax returns where the adjusted gross income exceeded $1 million will be subject to computer audit. For a particular year, a CPA completed 16 returns where the adjusted gross income exceeds $1 million.
a.) Which probability model does this situation follow?
b.) What is the probability that exactly one of these returns is audited?

I realize that A is just asking me for a probability formula that I will use to solve for in B. But I don't get how I can solve B if I don't have the total number of audits completed.
Please help me! I would greatly appreciate it!


TS Contributor
you could interpret the statement to mean that audits are picked randomly and and any return of more the 1 million usd has a 15% chance of being picked.

Then the answers should be easy.