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
Circle $A$ has a diameter of 12 inches and circle $B$ has a diameter of 22 inches. What is the ratio of the area of circle $A$ to the area of circle $B$? Express your answer as a common fraction.
user
test