Final answer:
Insufficient information to find a formula for s_n; details regarding the sequence type or rule are required.
Step-by-step explanation:
The question is asking to find a formula for s_n when the first two terms are given as (4/5) and (5/9). However, the information provided is insufficient to determine the type of sequence (whether it is arithmetic, geometric, or another form). Without additional information about the rule that generates the sequence, we cannot accurately answer this question or find a formula for s_n. To provide an answer, we would need to know the common difference for an arithmetic sequence, the common ratio for a geometric sequence, or other specific rules that define the progression of the sequence.