1. If the front of the red car is used as a reference point, how far away is the white van?

-36 m

Explanation:

In the diagram, the front of the black car is used as reference point which is point 0. The distance from the black car to the front of the red car is 15 m while the distance from the black car to the white van is - 21 m. The negative sign means the white van is behind the black car.

If the red car is used as the reference (point 0), the distance from the black car to the red car would be -15 m and the distance from the black car to the white van would be -21 m. Hence:

Distance from red car to white van = distance from the black car to the red car  + distance from the black car to the white van = -15 + (-21)

Distance from red car to white van = -15 - 21 = -36 m