I need help solving this problem......anyone help!

Marginal revenue. A defense attorney charges her client $4000 plus $120 per hour. The formula R= 120n + 4000 gives her revenue in dollars for n hours of work.

What is her revenue for 100 hours of work?$16,000

What is her revenue for 101 hours of work? $16,120

By how much did the one extra hour of work increase the revenue? The increase in revenue is called the marginal revenue for