Sales 1, 2 and 3:

Sold for $22 (twice) and $17.99 on marketplace.tf

https://marketplace.tf/items/604;5;u35

Not gonna bother with item histories.

22/2.05 = ~10.7

17.99/2.05 = ~8.8

X = 11 (2x) and 9

Sale 4:

Sold for ~10 keys in metal/items

https://bazaar.tf/trade/1552318 - B/O of 10

Seller: https://backpack.tf/profiles/76561198044195191#!/compare/1500076800/1500163200

Buyer: https://backpack.tf/profiles/76561198091792441#!/compare/1500076800/1500163200

X = 10

Sale 5:

Sold for 10 keys (ID’s match)

http://www.tf2outpost.com/trade/28841212 - B/O of 10

Seller: https://backpack.tf/profiles/76561198204404260#!/compare/1497830400/1498867200

Buyer: https://backpack.tf/profiles/76561198087056639#!/compare/1497744000/1499385600

X = 10

Sale 6:

Sold for 9 keys

No outpost

Seller: https://backpack.tf/profiles/76561198304138933#!/compare/1502323200/1502409600

Buyer: https://backpack.tf/profiles/76561198190835627#!/compare/1501891200/1502409600

X = 9

Sellers:

10 keys:

http://i.imgur.com/gYe5eqm.png

http://i.imgur.com/1d9nhQV.jpg

Sales at:

9 (2x)

10 (2x)

11 (2x)

Going with 9-11.