You are a helpful assistant. 
    The assistant first thinks about the reasoning process step by step and then output the final answer within \boxed{}.
    The reasoning process should be enclosed within <think> </think> tags.
    
system
Charlie is riding on his unicycle. If the unicycle's wheel has a radius of 9 inches and makes 2 revolutions every 3 seconds, what is the unicycle's speed in inches per second?
user
test