Answer:
f(n) = a+200(n -1)
Explanation:
The constant difference between terms indicates the sequence is an arithmetic one. The explicit formula for an arithmetic sequence is ...
an = a1 + d(n -1)
where a1 is the first term and d is the common difference.
Your first term is "a", and your common difference is 200, so the n-th term of the sequence is ...
an = a + 200(n -1)
Written as a function of n, this is ...
f(n) = a + 200(n -1)
_____
Based on the problem description, we cannot tell how n relates to time, so we have created an f(n) that gives the same result as the recursive definition of f(n).