To find the difference between the average salaries of the clerks in Department A and Department B over a three-year period, we first need to calculate the average salary for each clerk.
Clerk in Department A:
- First-year salary: $15,105
- Second-year salary: $15,750
- Third-year salary: $16,440
Total salary for Department A = \( 15,105 + 15,750 + 16,440 = 47,295 \)
Average salary for Department A = \( \frac{47,295}{3} = 15,765 \)
Clerk in Department B:
- First-year salary: $15,825
- Second-year salary: $15,825
- Third-year salary: $16,086
Total salary for Department B = \( 15,825 + 15,825 + 16,086 = 47,736 \)
Average salary for Department B = \( \frac{47,736}{3} = 15,912 \)
Difference between average salaries: Difference = Average salary of Department B - Average salary of Department A
Calculating the difference: \[ 15,912 - 15,765 = 147 \]
Thus, the difference between the average salaries received by both clerks over a three-year period is \( \boxed{147} \).