Precalculus please help

Which equation and solution can be used to solve this problem? thirteen less than a number is sixteen. 13-n=16: add 13 to both sides. the answer is 29. n+13=16: subtract 13 from both sides. the answer is 3. n+16=13 subtract 13 from both sides. the answer is 3. n-13=16: add 13 to both sides. the answer is 29.

You are at a restaurant and owe $38 for your meal. you want to leave a 20% tip. how much will your tip be?

Use circumcenter theorem to solve for the given values