Analyse the following problem in a way that ensures you to have reached the correct answer. Four robotic mini cars have to be transerred to a new location along a track. The only way to move the cars is to couple together two of the cars at atime with the only existing coupling device. The combination will then move to the new location with the speed of the slower car. One of the cars is left to the new location and another one will move back with the coupling device. This will take place until all the cars are in the new location. The transfer times of the cars are 15, 12, 6 and 3 minutes. What is the minimum total transfer time (new location+back+new..)? Explain your strategy by which you can be sure that you have found the correct answer to the problem. Make your strat egy visible.