You could show the map images with the associated numbers and invite children to suggest what the numbers mean. (This may provoke a discussion about how miles related to kilometres!)
Then set learners off on the challenges. You could suggest that, rather than attempting all of the calculations, pairs could decide which they think would be the easiest to work out and which would be the hardest, and why.
After a suitable period of time, you could invite pairs to join with another pair and compare their thoughts. If pairs do not agree on which is the easiest/hardest, challenge them to try to persuade the other pair that their 'ranking' is better. This will require knowledge of a range of calculation methods and sound reasoning.
How did you work this out?
If you wrote it down to work it out can you show me and talk me through it?
Although unrelated to the main questions you might like to make use of these maps to discuss why the 'straight' lines of the 'as the crow flies' are drawn as various curves.