How do I average 2 columns in SQL?

Question

While the rest of the code is functional, I can't figure out how to average the "Total Purchases" using the "Number of Purchases" to find the "Average Purchase Amount".

--- Query ---

SELECT C.CUS_CODE,
       C.CUS_BALANCE,
       ROUND(SUM(L.LINE_UNITS * L.LINE_PRICE), 2) AS "Total Purchases",
       COUNT(L.LINE_NUMBER) AS "Number of Purchases",
       AVG("Total Purchases") as "Average Purchase Amount"
  FROM CUSTOMER AS C
 RIGHT JOIN INVOICE AS I
    ON C.CUS_CODE = I.CUS_CODE
 RIGHT JOIN LINE AS L
    ON I.INV_NUMBER = L.INV_NUMBER
 WHERE L.INV_NUMBER = I.INV_NUMBER
 GROUP BY CUS_CODE, "Number of Purchases"

I've tried using the AVG() function with "Total Purchases" and grouping by "Number of Purchases" alias's but the query returns a 0 in each "Average Purchase Amount" column.

The output should represent the following:

Answer 1

SELECT CUS_CODE, CUS_BALANCE, 
       Total AS "Total Purchases", 
       Number as "Number of Purchases", 
       ROUND((Total/Number),2) as "Average Purchase Amount"

FROM    (SELECT C.CUS_CODE, 
        C.CUS_BALANCE, 
        ROUND(SUM(L.LINE_UNITS*L.LINE_PRICE),2) AS Total,
        COUNT(L.LINE_NUMBER) AS Number
       
       
        FROM CUSTOMER AS C

        RIGHT JOIN INVOICE AS I 
        ON C.CUS_CODE = I.CUS_CODE

        RIGHT JOIN LINE AS L
        ON I.INV_NUMBER = L.INV_NUMBER

        WHERE L.INV_NUMBER = I.INV_NUMBER

        GROUP BY CUS_CODE, "Total Purchases"
        ) AS A