Two ships A and B are `10 km` apart on a line running south to north. Ship A farther north is streaming west at `20 km//h` and ship B is streaming north at `20 km//h.` What is their distance of closest approach and how long do they take to reach it?

Explanation

To solve the problem of the two ships A and B, we will follow these steps:

### Step 1: Understand the motion of the ships
- Ship A is moving west at a speed of 20 km/h.
- Ship B is moving north at a speed of 20 km/h.
- The initial distance between the two ships is 10 km, with Ship A located farther north than Ship B.

### Step 2: Set up the coordinate system
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