A ,motorboat can travel 30 km upstream and 28 km downstream in 7 h. It can travel 21 km upstream and return in 5 h. Find the speed of the boat in still water and the speed of the stream.

Explanation

To solve the problem, we need to find the speed of the boat in still water (let's denote it as \( x \)) and the speed of the stream (let's denote it as \( y \)). We will use the information given in the problem to set up two equations.

### Step 1: Set Up the Equations
1. **From the first condition**: The motorboat can travel 30 km upstream and 28 km downstream in 7 hours.
- Upstream speed = \( x - y \)
- Downstream speed = \( x + y \)
- Time taken to travel upstream = \( \frac{30}{x - y} \)
- Time taken to travel downstream = \( \frac{28}{x + y} \)
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