How to generate position from a table using EF

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C#

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

What I have tried:

//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();