Without any passengers, an aeroplane has a mass of 4200 kg. The plane has capacity to carry 120 passengers, and when there are 40 passengers on the plane, the total mass of the plane and passenger is 7480 kg. a) calculate the mean mass of passenger b) Hence, write an expression for un that gives the total mass of the plane and passengers when there are n passengers on board c) state the values of n for which your model is valid