avg () and Joins in mysql

[Erfan anjum]

hi,

i am using following query to fetch data from multiple tables now i want to get the average of fetched records.
like i want to get the average marks of IRFAN.

CAN ANYONE PLS TELL ME HOW TO USE AVG() IN THIS QUERY




$QUERY = "SELECT subject,FirstName,marks FROM subject,all_members,marks WHERE all_members.mid = marks.mid and subject.subjectid = marks.subjectid and marks>=40 and all_members.FirstName='irfan'";
$rs = mysql_query($QUERY);