Syntax error(missing operator) in query expression

Hello,
I created two fields for me to able to calculate the grades of the students. Why do I get this error in MS Access?
“Syntax error (missing operator) in query expression”
My query is Select [Quiz], [Homework] from Student Where [Average] = ([Quiz] + [Homework]);
Is there any other way to compute the average in another type of query? And do you experts have any suggestions on how to do it?
