Hello all I am not sure whether I understood this problem: If 40 passengers hire a special car on a train, they will be charged $8.00 each. For each passenger over the 40 this fare is cut by $0.10 apiece for all passengers. (eg 50 passengers would pay $7.00 each). How many passengers will produce the greatest income for the railroad? My solution (18 + 0.1n)*n = I(x) I ' (x) = 18 - 0.1n - 0.1n = -0.2n + 18 -0.2n = -18 n = 90 Is this correct? Thanks a lot!