
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
$A$ tells $B$: "Take any number. Write its digits in reverse order and subtract the smaller number from the larger one. Multiply this difference by any number. In the resulting product, cross out any non-zero digit and tell me the remaining number." $B$ responds with 35407, at which point $A$ identifies the crossed-out digit as 8. 

How did $A$ know this?

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