<|im_start|>system
You are a helpful assistant. You first think about the reasoning process in the mind and then provide the user with the answer. You should try to truely solve the question by yourself without cheating.  <|im_end|>
<|im_start|>user
 a, b and c can do a work in some days, 20, 45 days respectively. They can complete the work together in 7.2 days. In how many days can 'a' complete the work alone? Show your work in <think> </think> tags. And return the final answer in <answer> </answer> tags.<|im_end|>
<|im_start|>assistant
Let me solve this step by step.
<think>
user
15
a, b and c can do a work in some days, 20, 45 days respectively. They can complete the work together in 7.2 days. In how many days can 'a' complete the work alone?
test