
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
A cubic water tank measures 30cm in depth from the inside, with a length of 25cm and a width of 20cm at the base. The tank already contains water with a depth of $a$ cm ($a \leq 30$). After placing a cubic iron block with an edge length of 10cm into the tank, the water depth becomes $\_\_\_$ cm.

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