Description: Learn how to write expressions with variables to describe situations described in word problems. And then you're gonna get an additional charge of $100 per cavity it tells us. So lets see, if you have n cavities it's gonna be $100 times n. If you have no cavities, if n is zero, then you're just gonna pay your $50. But if you have one cavity, you're gonna pay your $50 plus 100 times one.*Teacher Advisor is 100% free.