Traveling toward each other (meeting problem)

Two cars are traveling toward each other on the same highway at 45 km/h and 55 km/h respectively. If they are 100 km away at 10 : 30am, when will they be 0 km apart?
You can demonstrate the problem by dragging the slider "time" .

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You can create an another problem by changing parameters like distance and velocity.
Drag the slider "dist" to change the value of the distance between points A and B.
Drag sliders related to velocity of cars to change the value of velocity (km/h).

G a SOSPg for IMSS, 8.4.2010, Created with GeoGebra