Answer:
f(n) = 6n + 12
Step-by-step explanation:
There is a common difference in consecutive number of seats, that is
42 - 36 = 36 - 30 = 30 - 24 = 24 - 18 = 6
This indicates the sequence is arithmetic with nth term
= a₁ + (n - 1)d
where a₁ is the first term and d the common difference
Here a₁ = 18 and d = 6 , then
f(n) = 18 + 6(n - 1) = 18 + 6n - 6 = 6n + 12