Easy Cost Planning

Hi Folks,

I have one doubt when I was doing easy cost planning in Internal process,

1. I have selected Catagories E and Sources is :- 1000 and Plant is 1000

2. Given Quantity 10, and press enter then automatically system will calculate amount is 3000/-

Here I need to know, how system calculate amount? , Means where  the system is pick the price?

In that plan I didn't give any cost center, But system cost plan has triggered to cost center.

Please give valuable suggestions.

Thanks

Venkat