Mr. wu is going to stock the concession stand for the little league playoffs. he knows he will need at least twice as many hamburger buns as hotdog buns. hamburger buns cost $0.45 each, and hotdog buns cost $0.40 each. he cannot spend more than $60 on buns. if x = the number of hamburger buns and y = the number of hotdog buns, which system of inequalities could be used to determine how many of each kind of bun mr. wu should purchase for the stand?