Assuming your headers are in row 1 and the data in A2:C6, use
SUMPRODUCT with double unary operators, comme ca:

=SUMPRODUCT(--($A$2:$A$6=13),--($B$2:$B$6="CA"),$C$2:$C$6)

This link
http://groups.google.com/group/micro...6bd4f93886f512
....explains the --, which is called a double unary operator. Very cool
stuff.