Ms Access SQL problem
You need to make SQL join Sale to Customer. There are two ways to approach this:

APPROACH #1

In SQL mode, add the Sale table to the FROM clause

SELECT [Customer].[CUSContact] FROM Customer,Sale
WHERE [Sale].[CUSID] = [Customer].[CUSID];


APPROACH #2

Open the QBE (Query-By-Example) Grid and add the Sale table. The graphical representation of the query should draw a line from the CUSID in the Customer table to the CUSID in the Sale table.

Give it a Try !!!

UPDATE 2014-03-10 14:43 EDT

I just looked at the image again. Perhaps the query should be this instead:

SELECT [Customer].[CUSContact] FROM Customer,Sale
WHERE [Sale].[CUSID] = [Customer].[CUSnum];