Project Invoice event

Summary

Which BU will be the AR invoice's BU?

Content

Situation:

1.Contract A : LE1 , BU1

2.Project A: LE1 , BU1

3.Project B : LE1 , BU2

4.Project A is associated with contractA line1 , Project B is associated wit contractA line2

Create two invoice event, one for contractA line1 project A ,another for contractA line2 project B,then generate invoice.

Question: What are the invoices' BU ?  Are the invoices' BU same as contractA or comes from projects?