X*0.9-215=X*0.8+125X=3400进价=3400*.9-215=2845
(215+125)/(0.9-0.8)*0.9-215=2845
设售价为X.成本为Y0.9X-Y=2150.8X-Y=-1250.9X-0.8X=215+125X=3400Y=2845成本=2845