Two boat A and B 20 km apart as shown. Boat a streaming east and boat B in north by `30 km//hr` then find shortest approach and time taken for it.

Explanation

To solve the problem of finding the shortest approach between two boats A and B that are 20 km apart, with boat A moving east and boat B moving north at a speed of 30 km/h, we can follow these steps:

### Step 1: Understand the motion of the boats
- Boat A is moving east at 30 km/h.
- Boat B is moving north at 30 km/h.
- The initial distance between the two boats is 20 km.

### Step 2: Set up the coordinate system
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