With what average speed must you drive your car if your average speed for the entire 23 km is to be 25 km/h?

25km/h

Explanation:

This is a trick question, the average speed in this case does not really depend on calculation or extrapolation, it just refers to an event that is yet to occur,

In other words, if you want to achieve an average speed of 25km/h for 23km, then you should drive your car at a constant speed of 25km/h, any variation in speed may cause a change in your average speed at the end.