Ok you know the distance between the car and truck, and you know their speeds and you need to find the time.
In terms of relative velocity, its just distance = relative velocity*time
But in case you're not familiar with relative velocity, look at it like this. Assume the car takes time T to overtake the truck. It moves a distance 25*T during this. The truck moves a distance 18*T in the meantime. Now, The car should move 37.5 m more than the truck to overtake it.