How do I create a list report using two Subject Areas?

I'm trying to create a simple list report using two Subject Areas, but I just cannot achieve what I want to.  I have data in Service Requests and matching data in Custom Object 3.  The link between the two tables is the Service Request Priority and Type, and these have a link to attribute columns 1 and 2 in Custom Object 3.  The report I want to produce would display the value of a third attribute in Custom Object 3.

If I was writing a standard SQL query, it would look something like this:

SELECT A.SR_NUMBER, B.ATTR_3

FROM SERVICE_REQUESTS A, CUSTOM_OBJECT_3 B