Can any help out Passing Multiple drop down values in php

I have drop down list which populate rows such as primary, high school, PUC. If user selected as primary i need to show all the students which are in class-1 to class-7 students from the table "student_info".

Similarly if it's high school,I need to display students who are in class-7 to class-10.

Now from Table "student_info". How I have to filter students which comes under primary through "Class" column only..

via Chebli Mohamed