Querry About Sales Commisions

[wkalo]

Hi There
I Need A Querry For Commission Sales.
I Have 10 Items 7 Items At 2% Of Commission 3 At 4%. Each Salesman Have To reach A Min Of 5000 USD Of Sales Per Month Then All Sales Above That Amount Commission Will Be Calculated.
I Need A Querry To Calculate Sales And If Salesman reached The Min Sales Commission Is Calculated .

Any Help ???????
Thanks