How to generate position from a table using EF

Question

Good day All, I need your help, I want to generate Position from a list of record for a particular user

 

//I have a table Named Mark
MarkID     UserId      SubjectName      TotalScore
1           20            English         60.00
2           21            English         70.00
3           20             Maths          80.00
4           21             Maths          80.00

// From the Table above i want to automatically generate Subject position for each each user in a gridview like this
MarkID     UserId      SubjectName      TotalScore     Postition
1           20            English         60.00         2
3           20             Maths          80.00         1

How do i automatically generate the subject position on it

Normally this is what i have tried so far to get the list of a particular record
var acc  = from c in cdc.Marks where c.userId = "20" select c).tolist();
gridview1.datasource = acc;
gridview.datindind();

//The above code only generate the student records and displays it on a gridview but automatically generating Position without is what i am looking for.. Please your help is really needed..

Thanks in advance