It looks like you've provided the distance $d = 400 \, \text{km}$ and the time $t = 4 \, \text{hours}$.

If you're looking for the speed, we can calculate it using the formula:

$\text{Speed} = \frac{\text{Distance}}{\text{Time}}$

Substituting the given values:

$\text{Speed} = \frac{400 \, \text{km}}{4 \, \text{hours}} = 100 \, \text{km/h}$

So, the speed is 100 km/h.

Would you like more details or have any specific questions about this?

Here are 5 related questions to consider:

1. How do you convert speed units, for example from km/h to m/s?
2. What is the formula for calculating average speed over multiple segments of a journey?
3. How would the speed change if the distance was increased to 600 km but the time remained the same?
4. What factors can affect the calculation of real-world speed (e.g., road conditions, traffic)?
5. How can you use this speed to calculate the time needed for a different distance?

Tip: To improve speed calculations, always double-check that the time and distance units are consistent!