Calculate percentage of marks

Question

Hi!!
I am making an application for generating report containing marks of students in various subjects with percentage and corresponding grades.
I have two forms one for "Entering marks" and other for "generating result" .
For "Entering marks" ,there are 5 combos and a textbox. From combos we can select type of exam(First Term,Half yearly and final term), class, section, subject,student and for this particular exam-class-section-subject-student combination I enter marks through textbox, which gets saved in database.
For generating result ,there are 4 combos for selecting type of exam(First Term,Half yearly and final term), selecting class , section,and student. Now for the selected student I want to create report which displays all the marks in various subjects along with percentage and grade.
Now how can I collect all marks of all subjects of any particular student and calculate percentage of it .
Kindly provide some solution...............