Help first one to get right wins

Four airplanes carrying a total of 400 passengersarrive at the detroit airport. the airplanes carry, respectively,50, 80, 110, and 160 passengers.a) one of the 400 passengers is selected uniformly at random.let x denote the number of passengers that were on theairplane carrying the randomly selected passenger. find var(x)for x as given in the problemb) one of the 4 airplane drivers is also selected uniformly atrandom. let y denote the number of passengers on the chosen driver’s airplane. find var(y) for y as given in the problem

Solve for x: 5/3 x = 20/21 it's fraction. remember to simplify your fraction

Using only the digits 5, 6, 7, 8, how many different three digit numbers can be formed if no digit is repeated in a number?