expression in Report view in asp.net

Hi 

I have problem in Report viewer.  I am using the expression to filter the value. I explain my scenario.

I want sum the amount for particular category. I have student database. I need the sum the paid amount for exam fee only.

=SUM(Fields!Amount.Value, "DataSet1") . It sums all amount. But I need to sum EXAM FEE only. Please help me how to do this

Thank  you

Maideen