FileMaker Pro simple function

I am looking for a Claris FileMaker Pro developer. I do not want to assign a larger project without some personal history with the person i will be working with. This request is not for the whole project, just a for a function and if you really know Filemaker code this should be really easy task. The initial task and your bid applies to: I have 2 tables "Orders" and "Inventory". I want add a column "Sold Past 30 Days" to "Inventory" that get the sales history from the past 30 days. All products in "Inventory" have a unique ID that can match from "Orders". "Orders" table include all neccecery data like "OrderDate", "QtySold". I want the sum of the "QtySold" past 30 days. Matching ID: Lager::Property EAN Order::identifier Needed: Order::created at Order::quantity Result should be showed in: 
 Lager::SoldQty30Days 
 Something like SQL-ish(i am no coder): Lager::SoldQty30Days = SELECT SUM (Order::quantity) FROM Order JOIN Lager ON Order::identifier = Lager::Property EAN WHERE Lager::Property EAN = Order::identifier AND Order::created <= (30daysMax) Filemaker project containing data will be provided.