I'm not sure if I'm missing something in the case study, but could someone clarify the difference between the Days attribute in the HiredVehicle relation and the hireDays attribute in the Booking relation? Are they referring to the same concept (The number of days the client is hiring the car)? If they are, why are they both listed as different attributes? Also wondering how the derived attribute finalcost is supposed to be calculated - Is the rentalPrice in the Daily Tariff assumed to be a flat rate of $3 per day? So that multiplied by # of days it is hired? (again which 'days' would I reference) This is the same issue I am finding with cost in the insurance relation. Thanks :)