Computing Cost for a Probability Problem

#1
Hi all, new here. Not sure if I post this to the right place. Just to preface, this is an area where I am pretty weak in.

I play a game called Maplestory. In this game, there are weapons. You can power up the weapons by enhancing them. The probabilities of success are different for enhancing from level 0 to 1, 1 to 2, so on and so forth. The probabilities are in the google sheets below.

Each enhancement has an associated cost to it.

Enhancement from level 10 onwards has a chance where the level will drop, and also a chance where the weapon breaks. When it breaks, you got to repair it and that costs $5 million.

My objective is to compute the cost to reach level 17, 18 and 19 for a weapon.

Now, I am able to compute (as shown in the right side of the google sheets) the associated costs to reach a certain level for the weapon as well as the average cost of repair.

However, these computations do not take into account degradation. This is where I got stuck.

Degradation = dropping down a level. If I am enhancing a level 12 to 13, and it degrades, it goes down to 11. So I have to account the cost from level 11 to 12 again. And there is also a chance that it degrades again.

Hope that someone can advise me how I can accurately compute this.

Please let me know if such posts are not allowed here. Thanks!

https://docs.google.com/spreadsheets/d/1KbTufsu9rRcTwtXJN5BNFxvjO9VmjCaNFXVxV5yawTM/edit#gid=0
 
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