19. Determine the intervals of concavity and the points of inflection for the following function: (8 marks) f(x)=x4+4x3 -18x2 +12x-12 20. An express railroad train between two cities carries 10,000 passengers per year for a one way fare of $50. If the fare goes up, ridership will decrease because more people will drive. It is estimated that each $10 increase in the fare will result in 1000 fewer passengers per year. What fare will maximize revenue? (6 marks)