Answer: 20%
Step-by-step explanation: Since the number changes from 15 to 18, it's getting bigger which means it increases. To find the percent increase, we use the formula shown.
The amount of change is the difference between the two numbers. In this case, we would subtract 18 - 15 which equals 3. Then, we put 3 over our original number which is 15.
3 ÷ 15 = 0.2
Now, we need the percent increase which means we need to write 0.2 as a percent by moving the decimal point two places to the right to get 20%.
Therefore, the percent increase is 20%