Write the equation in standard form for the hyperbola with vertices (-12,0) and (12,0) and foci (-15,0) and (15,0)

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

Which shows the correct solution of the equation 1/2a+2/3b=50, when b=30?

We just started the introduction into circles and i have no idea how to do this.