
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
1. Two ports A and B are 75 km apart. It takes a boat 3 hours to travel from A to B downstream and 5 hours to travel from B to A upstream. Find the boat's speed in still water and the speed of the current.
2. If ports A and B are S km apart, and a boat takes a hours to travel from A to B downstream and b hours to travel from B to A upstream,
   ① find the boat's speed in still water and the speed of the current, expressed in terms of a, b, and S;
   ② calculate the time it takes for a log to drift from port A to B downstream, expressed in terms of a and b.

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