
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 that the cost per unit of a certain product is $6$ yuan, and the selling price per unit is $x$ yuan $(x > 6)$, with an annual sales volume of $u$ ten thousand units. If $21-u$ is directly proportional to $x^2-6x$, and when the selling price per unit is $10$ yuan, the annual sales volume is $\frac{23}{3}$ ten thousand units.

   (Ⅰ) Find the function relationship between the annual sales profit $y$ (in ten thousand yuan) and the selling price per unit $x$ (in yuan);

   (Ⅱ) Find the selling price per unit that maximizes the annual sales profit, and calculate the maximum annual sales profit.

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