Write each of the following using appropriate sing `+` or -:
An aeroplane is flying at a height of 3500 m above sea level .

Answer

To solve the problem of writing the height of an airplane flying above sea level using the appropriate sign, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Context**: The problem states that an airplane is flying at a height of 3500 meters above sea level. We need to represent this height using a sign.

**Hint**: Think about what 'above sea level' means in terms of positive and negative values.

2. **Identify the Reference Point**: The reference point here is sea level. Heights above sea level are considered positive, while depths below sea level are considered negative.

**Hint**: Remember that sea level is the baseline for measuring heights and depths.

3. **Assign the Appropriate Sign**: Since the airplane is flying above sea level, we will use a positive sign (+) to represent this height.

**Hint**: Positive values indicate something that is above the reference point.

4. **Write the Expression**: Therefore, we can write the height of the airplane as +3500 m.

**Hint**: Make sure to include the unit (meters) along with the sign and value.

### Final Answer:
The height of the airplane is represented as **+3500 m**.