
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
An observation station is located at point $C$, which is to the south and west by $20^{\circ}$ from city $A$. A road that heads south-east by $40^{\circ}$ starts from city $A$. At point $C$, it is measured that a person at point $B$, $31 \, \text{km}$ away from $C$ along the road, is walking towards city $A$. After walking $20 \, \text{km}$, the person reaches point $D$, where the distance between $C$ and $D$ is $21 \, \text{km}$. How many more kilometers does this person need to walk to reach city $A$?

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