
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given an arithmetic sequence $\{a_n\}$ satisfies $a_2+a_3+a_4=15$ and $a_4+a_6=18$. The sum of the first $n$ terms of sequence $\{b_n\}$ is $S$, and it satisfies $S_n=2b_n-2$.
$(1)$ Find the general formula for sequences $\{a_n\}$ and $\{b_n\}$;
$(2)$ Sequence $\{c_n\}$ satisfies $c_n= \frac {a_n}{b_n}$, find the sum of the first $n$ terms of sequence $\{c_n\}$.

Present the answer in LaTex format: \boxed{Your answer}
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