
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 the function $f(x)=|2x-4|+|x+1|$,  
(I) Solve the inequality $f(x)\leqslant 9$;  
(II) If the solution set of the inequality $f(x) < 2x+a$ is $A$, $B=\{x|x^{2}-3x < 0\}$, and it satisfies $B\subseteq A$, find the range of the real number $a$.

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