Yorea Deah hypothetical

Inspired by my chevruta study today in Basar B'Chalav.

Imagine you have a new 8 ounce metal spoon, which you use to stir an ounce of melted margarine. Later that day you take out two spoonfuls of beef stew with the same spoon. When you go to spread margarine on your bread, you realize that it is dairy margarine.

How many ounces of Beef Stew has to be in the pot in order to nullify the spoon and still be kosher?

Highlight the area below for my answer.
540 oz. The relevant halachot are

1. If you know exactly how much food a kli (utensil, like a spoon or a pot) has absorbed you can use that amount instead of the total size of the kli.
2. If you dip a mlichig spoon twice into a meat pot you need 120 rather than 60.
3. So the first time you dip the spoon, you need 60 * 1 oz to nullify the diary in the spoon. At the same time 8 oz of bliot from the meat enter into the spoon and become a chanan of milk and meat. So the next time you dip the spoon, you need 8 oz * 60 to nullify the spoon which is now full of milk and meat. 60 + 480 = 540