800x+600y=7400, x, y must be a positive integer, x∈,

(2) There are X middle school students and Y primary school students.

X = 1，Y = 1 1，X = 2，Y = 29/3，X = 3，Y = 9，X = 4，Y = 7，X = 5，Y = 17/3。

So * * * has x= 1, y =11; x=3，y = 9； x=4，y = 7； X = 7, y = 3, and * * * are four schemes.