What is the standard error of the sampling distribution of the sample mean?

Solve |x| > -9 a) {x|x< -9 or x> 9} b) all reals c) no solution

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

What is the result of adding the system of equations? 2x+y=4 3x-y=6