If the speed of a boat in still water is 8 km/h and the rate of stream is 4 km/h, then find upstream speed of the boat.

Answer

To solve the problem of finding the upstream speed of the boat, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Data:**
- Speed of the boat in still water (B) = 8 km/h
- Speed of the stream (S) = 4 km/h

2. **Understand Upstream Speed:**
- Upstream speed refers to the speed of the boat when it is moving against the current of the stream. This means that the speed of the stream will reduce the effective speed of the boat.

3. **Formula for Upstream Speed:**
- The formula to calculate the upstream speed of the boat is:
\[ \text{Upstream Speed} = \text{Speed of the Boat} - \text{Speed of the Stream} \]
- In mathematical terms:
\[ \text{Upstream Speed} = B - S \]

4. **Substitute the Values:**
- Now, substitute the values of B and S into the formula:
\[ \text{Upstream Speed} = 8 \text{ km/h} - 4 \text{ km/h} \]

5. **Calculate the Upstream Speed:**
- Perform the subtraction:
\[ \text{Upstream Speed} = 4 \text{ km/h} \]

6. **Final Answer:**
- Therefore, the upstream speed of the boat is **4 km/h**.