
Answer: Â C) f(n) = 20 + 2(n - 1)
Step-by-step explanation:
The explicit formula is: [tex]a_n=a_1+d(n-1)[/tex] Â Â where
Given: In the first year he paid $20 Â --> [tex]a_1[/tex] = 20
     Dues increase $2 each year --> d = 2
[tex]a_n[/tex] = 20 + 2(n - 1)