Find last year's salary if, after a 5% pay raise, this year's salary is $38,325?

5% of 38325 is 1916.25 

subtract the answer from this years salary 

38325 
- 1916.25 
 that would be 36408.75

now add comma and dollar sign and  last year's salary is $36,408.75

To answer the question above,
This means that
This year my salary is: 105% ( up 5% from 100%) ;
Salary = $31500 
and last year. 100% ( base year) ; Let the Salary = $x 

Now let us solve, 
x / 100 = 31500/105 
so x = 31500 * 100/105 =
$30 000
I hope my answer helped you I've included the formula on how I got the answer.