Using last month.

Sales 1 & 2:

Sold for $37.88 and $37.85 on marketplace.tf

https://marketplace.tf/items/477;5;u3005

https://backpack.tf/item/6618589832

Couldn’t find item histories

http://manicbot.me/keyprice/?at=2018-08-14

37.88/1.87 = ~20.26

37.85/1.87 = ~20.24

X = 20 (2x)

Sale 3:

Sold for 18 keys

Seller: https://backpack.tf/profiles/76561198118177331#!/compare/1534896000/1534982400

Buyer: https://backpack.tf/profiles/76561198097816819#!/compare/1534896000/1534982400

https://backpack.tf/item/6618589832

X = 18

Sale 4:

Sold for 17 keys

Seller: https://backpack.tf/profiles/76561198082899111#!/compare/1534291200/1534377600

Buyer: https://backpack.tf/profiles/76561198050838732#!/compare/1534204800/1534550400

https://backpack.tf/item/6481140413

X = 17

Sale 5:

Sold to a bot for 9 keys

Seller: https://backpack.tf/profiles/76561198097816819#!/compare/1534032000/1534118400

Buyer: https://backpack.tf/profiles/76561198334598690#!/compare/1534032000/1534118400

https://backpack.tf/item/1557022681

https://i.imgur.com/0nFD7M1.png

X = 9

Sellers:

https://i.imgur.com/58c1SGr.png

https://i.imgur.com/0oPB0Og.png

https://backpack.tf/item/1557022681 - 20

https://backpack.tf/item/6790750445 - 20

https://backpack.tf/item/1564567865 - 22

https://backpack.tf/item/1816700458 - 25

https://backpack.tf/item/3301709696 - 30

https://backpack.tf/item/1127213937 - 40

Sales at:

9

17

18

20 (2x)

9 is a single sale to a quickbuyer, and is significantly lower than the other sales. Excluding 9.

Going with 17-20.