一个文本文件（file15.txt,若干位同学的数学成绩，文件中每行的内容按照顺序为：学号，班级数学成绩，姓名，请完成以下问题；

1.将文件中的内容全部显示到窗体，并统计总人数。

2.统计数学成绩的平均分。

3.统计各个班级的平均分。

-A text file (file15. Some students, TXT files in the mathematics achievement, in accordance with the contents of each order: math class, student id, name, please complete the following questions,

1. The content of the document, and statistics show that form the total number.

2 the math statistics.

3 each class of statistics.