Charlie rented a truck for one day. there was a base fee of $17.99 , and there was an additional charge of 81 cents for each mile driven. charlie had to pay $213.20 when he returned the truck. for how many miles did he drive the truck?

To solve this, you need to start by writing out an equation. Since there was a base fee of 17.99, and .81 cents for each mile driven, you'll have 17.99 + .81x, where x represents how many miles driven. If he paid 213.20 at the end, you know that's what 17.99 + .81x will have to equal.
So you have:
17.99 + .81x = 213.20

Now you need to solve for x. Do you know how to solve for x here?