Find a polynomial function f(n) such that f(1), f(2), , f(8) is the following sequence.2, 8, 14, 20, 26, 32, 38, 44

We can recognize the sequence is an arithmetic progression by noticing that the common difference between each term is 6.

where f(n) is the sequence 
n is the term number
d is the common difference 
and a is the starting term

We are well aware that our starting term, and hence a, is 2 and our difference, and hence d, is 6.
So our polynomial function is