Answer: 20%
Step-by-step explanation:
To solve this problem you must apply the proccedure shown below:
1. You must apply the following formula (Let's call the percent of increase:[tex]x[/tex]):
[tex]x=(\frac{increase}{original})(100)[/tex]
[tex]increase=18-15\\original=15[/tex]
2. Substitute values and solve:
[tex]x=(\frac{18-15}{15})(100)\\[/tex]
[tex]x=20[/tex]%