A boat goes `30` km upstream and `44` km downstream in `10` hours. In `13` hours, it can go `40` km upstream and `55` km downstream. Determine the speed of the stream and that of the boat in still water.

Explanation

To solve the problem, we need to determine the speed of the boat in still water (let's denote it as \( x \) km/h) and the speed of the stream (denote it as \( y \) km/h).

### Step 1: Set Up the Equations
1. **Upstream Speed**: When the boat is going upstream, its effective speed is \( x - y \) km/h.
2. **Downstream Speed**: When the boat is going downstream, its effective speed is \( x + y \) km/h.

From the problem, we have two scenarios:

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