Another expression in a query

Using query designer I need code to:

Sum the totals of [NumberOfHours] where PublicActivityCode] = "GT" or "ST".

It needs to be an expression because I have more of these types of fields to add.


An expert already helped me wit another code which worked for that one.  It was:

TouringCount: Sum(Abs([PublicActivityCode]="GT" Or [PublicActivityCode]="ST"))

So it has to be something like: (but the syntax is wrong)

TotalHours: Sum(Abs(NumberOfHours] WHERE ([PublicActivityCode]="GT" Or [PublicActivityCode]="ST"))

--Steve