The variable x represents the number of long-sleeve shirts nancy bought and the variable y represents the number of short-sleeve shirts she bought. nancy bought 531 shirts for her business. she bought 2 times as many short-sleeve shirts as long-sleeve shirts. how many of each type of shirt did she buy? which system of equations models this problem? {x−y=531 y=2x {x+y=2 y=531x {x+2y=531 y=2x {x+y=531 y=2x