A Chain of Events

Three friends, Davina, Jolene and Katie, set out

to the Hoppings fairground, travelling on their

three bikes. They lock up the bikes and go to

enjoy their day. When they return, they find two

of the bikes have disappeared. Assuming only

one person can ride the remaining bike at a time,

and that it is 12 miles back home, how should

they proceed, to be fair to each other so each

person ends up walking the same distance? The

bike has a speedometer with a mileage counter.

What if only one bike had been stolen?

please answer fast