This way
SQL
DECLARE @tblStudent TABLE (NAME VARCHAR(20), Subject1 INT, Subject2 INT)
INSERT INTO @tblStudent VALUES('A',10,20)
INSERT INTO @tblStudent VALUES('B',12,24)
INSERT INTO @tblStudent VALUES('C',15,22)
INSERT INTO @tblStudent VALUES('D',18,9)
SELECT Name, Subject1 + Subject2 as Total FROM @tblStudent ORDER By Total DESC
Output
Name Total
C 37
B 36
A 30
D 27