Problem with calculation of Yearly and Monthly sales targets with conditions!

[CopperKnife]

Hi,
Good morning all,

I have a problem with calculation of my Sales Targets in PowerPivot.
I have two Tables; dimProducts, OrderBook.

Columns for dimProducts:

ProdID	Cost	Price	MonthlyGoal	YearlyGoal	Commission
1	1200	1300	50	400	3%
2	1456	1532	40	350	2%
3	1832	2345	30	300	2.5%
4	1064	1245	70	900	4%

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</tbody>

Columns for OrderBook:

OrderDate	ProdID	SalesPerson	Qty	MonthlySales	YearlySales
7/13/2012	1	Ram	12	???????	?????
8/14/2012	2	Robert	13	??????	??????
9/1/2012	3	Raheem	14	???????	?????

<tbody>
</tbody>

I need to calculate both Monthly sales and Yearly Sales for a specif ic ProductID and for a specific SalesPerson row wise?

I have relationship with ProdID columns in both the Tables.

I am perplexed on which formula to use for this question.

Thanks