阅读材料，完成任务。

    My uncle Jack is an interesting man. When he speaks, his mustache（胡子） always dances. It is so funny. He wears glasses and a funny hat.

    I don't like my boss（老板） at all. He is heavy with two small eyes. I think his glasses are too small for him.

— Look, the salesman（商人） is coming.

— Which one?

— The one with short black hair. He always takes his umbrella(雨伞) and suitcase(旅行箱). And his tie is very ugly.

— What are you doing, Lucy? Look at your pants. They are so dirty!

— I am doing some cleaning. Don't come here, Jane. Your beautiful skirt will be dirty.

甲、乙两名同学在解方程组 $\{\begin{array}{c}mx+y=5\\ 2x-ny=13\end{array}$ 时，甲解题时看错了m，解得 $\{\begin{array}{c}x=\frac{7}{2}\\ y=-2\end{array}$ ；乙解题时看错了n，解得 $\{\begin{array}{c}x=3\\ y=-7\end{array}$ ．请你以上两种结果，求出原方程组的正确解．