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
Given $x\neq0$, find the positive value of $b$ such that the equation $\frac 3x+\frac x3=b$ will have exactly one solution.
user
test