Modern commercial airliners are largely made of aluminum, a light and strong metal. But the fact that aluminum is cheap enough that airplanes can be made out of it is a bit of historical luck. Before the discovery of the Hall-Hroult process in 1886 , aluminum was as rare and expensive as gold. What would happen if airplanes had to be made of steel? The fuselage of the Boeing 747, which can carry 400 passengers, is approximately a hollow aluminum cylinder without ends, 70.7m long, 6.5m wide, and 2.5mm thick (see sketch at right). Suppose this fuselage was made of steel (density 7.87g/cm3 ) instead of aluminum (density 2.70g/cm3 ), and let's say the average passenger has a mass of 81kg. We'll also assume the engines can't lift any greater mass than they already do. Calculate the number of passengers that the Boeing 747 could carry if its fuselage was made of steel