题目《九章算术》中记载:"今有共买羊,人出五,不足四十五;人出七,不足三,问人数、羊价各几何?"其大意是:今有人合伙买羊,若每人出555钱,还差454545钱;若每人出777钱,还差333钱,问合伙人数、羊价各是多少?设合伙人数为xxx人,羊价为yyy钱,根据题意,可列方程组为( )A.{y=5x+45y=7x+3\left\{\begin{array}{l}{y=5x+45}\\{y=7x+3}\end{array}\right.{y=5x+45y=7x+3B.{y=5x−45y=7x+3\left\{\begin{array}{l}{y=5x-45}\\{y=7x+3}\end{array}\right.{y=5x−45y=7x+3C.{y=5x+45y=7x−3\left\{\begin{array}{l}{y=5x+45}\\{y=7x-3}\end{array}\right.{y=5x+45y=7x−3D.{y=5x−45y=7x−3\left\{\begin{array}{l}{y=5x-45}\\{y=7x-3}\end{array}\right.{y=5x−45y=7x−3知识点:由实际问题抽象出二元一次方程组章节:方程与不等式 / 二元一次方程组