Math Help - Metric of cities

Let be the set of cities, Indicate which metric on must consider a traveller, if he moves in: a car, a plane, a train and a bike.

I don't get well the problem. How to proceed?

Originally Posted by Connected

Let be the set of cities, Indicate which metric on must consider a traveller, if he moves in: a car, a plane, a train and a bike.

I don't get well the problem. How to proceed?

This makes zero, absolutely no sense haha. Did you copy it wrong?

No, I copied it well.

Haha, for me doesn't make any sense too!