
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 stratified random sampling method is used to select a certain number of cars for investigation from three cities, A, B, and C, based on a proportional allocation. The total sales and the number of cars selected from each city are shown in the table below:

| City | Total Sales | Number Selected |
|------|-------------|-----------------|
| $A$  | $420$       | $m$             |
| $B$  | $280$       | $20$            |
| $C$  | $700$       | $n$             |

Determine the total sample size.

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