Sales 1-4:

Sold for $39.44, $35.99, $28 & $27.25 on marketplace.tf

https://marketplace.tf/items/99;5;u7

https://manic.tf/keyprice/?at=2018-10-21 - $35.99 / $1.8 = 19.99 keys

https://manic.tf/keyprice/?at=2018-10-25 - $28 / $1.8 = 15.56 keys

https://manic.tf/keyprice/?at=2018-12-02 - $27.25 / $1.71 = 15.94 keys

https://manic.tf/keyprice/?at=2018-12-27 - $39.44 / $1.79 = 22.03 keys

X = 22

X = 20

X = 16 (2x)

Sale 5:

Sold for 19 keys

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1545436800/1545523200

Buyer: https://backpack.tf/profiles/76561198107789076#!/compare/1545350400/1545696000

https://backpack.tf/item/3926341942

X = 19

Sellers:

https://i.imgur.com/sLlXZJ5.png

https://backpack.tf/item/277115576 - 20 keys

https://backpack.tf/item/6059188956 - 24 keys

Sales at:

16 (2x)

19

20

22

https://i.imgur.com/i72miIt.png - Buyer at 17 keys, and the 16 key sales would’ve gone to marketplace buy orders. Excluding 16.

22 is countered by the 2-month unsold at 20. Excluding 22.

Going with 19-20.