How to search a field with its nearest value

Databases
1

Hello all
i have a table which contains percentages of subjects.
i.e

 id | a | b | c | d
   1  | 15|20 |40 | 23

Now i have another record which have subject c highest value i.e c=35
i want to match it against the the other records which have in the range of 7 less than and 7 greater than the highest value
(where 7<c>7 ).

how can i make query to get the matching records.

sample query is 


    $query="select id from percent where (subject c is in the range less than 7 and greater than 7)
    

in my case if c=35 than this query should return the record with id 1 cause (7 greater than c) c=35+7=42 and in record with 
id 1 has c=40
2

Wouldn’t it be better to normalize that table? (id, subjectid, percentage)

Now i have another record which have subject c highest value i.e c=35

Another record? Where? Same table, other table, user input?

3

yes another record is of same table. why i am not normalize cause this table already contain a foreign key st_id

4

What is st_id?

How do you identify the row with the max c value to use?

5

okay i posted all the db design.
i have a student table(st_id, name …)
and percent table (id, subject a, b, c,d, st_id)

now first i search the percent table for specific student

$query="SELECT  a, b, c,d
FROM percent
WHERE st_id =1";
$rs=mysql_query($query) or die(mysql_error());
$row=mysql_fetch_assoc($rs);
arsort($row);
$keys = array_keys ($row);

This will find the highest percentage and its value
now my question is how can i find the match which is in the range 7 less and 7 greater than

6 
WHERE c > 35 - 7
AND c < 35 + 7