How to use 2 dataset in on matrix

Hi All,

I have 2 datasets:

YearMonth, Orders

2013-1-1,300

2014-1-1,200

YearMonth,Customers

2013-1-1,1000

2014-1-1,5000

I would like to use Matrix to show the average orders per customer

It looks like:

YearMonth Orders/Customers

How to achieve it?

Thanks.