If a person was 9 years old in 1 998, determine the age of that person in 2 009.
The difference between the person's age in 2009 and the person's age in 1998 is equal to the difference between the year 2009 and the year 1998.
Write an equation to represent the problem. Let represent the person's age in 2009, and solve for the value of .
So, the person's age in 2009 is 20.