分三种方案,设低档X套,中档(200-X)套 10X +15(200-X)=2800,得X=40 设低档X套,高档(200-X)套 10X+20(200-X)=2800,得X=120 设高档X套,中档(200-X)套 20X+15(200-X)=2800,得X=-40