The error means that you are trying to call a non static method in a static way, like maybe this one:
Journey.journeyCost(thisJourney);
Is journeyCost() declared static? Don't you mean instead thisJourney.journeyCost()?
Plus you should use getters and setters to modify and access your member variables, so instead of:
Journey.dayCharge = ...
you should have
Journey.setDayCharge(Journey.getDayCharge() + thisJourney.getCostOfJourney());
(setDayCharge and getDayCharge need to be static in this case)
