Set Default Value

hlw, im a Beginners... i create a table which column name is ID,NAME,SUBJECT,MARKS,STATUS. Now i want to set like this, if i put less than 30 in theMarks column the Status column automatically put 'Fail' and if i put up to 30 in theMarks column the Status column automatically put 'Pass'. Does anyone know how to do that?

THANKS...