Let me rephrase the question like this:
You attack an army of 9 angels with an improved stack. You attack with a hero with the stats 1-1-2-2. Your army can only consist of archers.
Question(s):
What is the minimum number of archers needed to make the angels form three stacks?
How do you calculate the strength of an archer army (which specific numbers should be taken into account) and how do you calculate the strength of an angel army (based on 9 angels or 6 + 3 archangels)?