which system of equations models this problem?

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?

a. x + y = 531
y = 2x

b. x - y = 531
y = 2x

c. x + 2y = 531
y = 2x

d. x + y = 2
y = 531x