Sale 1:

Sold for 9 keys

http://www.tf2outpost.com/trade/28085470 - B/O of 9

Seller: http://backpack.tf/profiles/76561198096014722#!/compare/1461456000/1461542400

Buyer: http://backpack.tf/profiles/76561198079628881#!/compare/1461456000/1461542400

X = 9

Sale 2:

Sold for Nuts n Bolts Pugilist Protector

http://www.tf2outpost.com/trade/28113326 - No B/O

Seller: http://backpack.tf/profiles/76561198079628881#!/compare/1461542400/1461628800

Buyer: http://backpack.tf/profiles/76561198084056439#!/compare/1461542400/1461628800

X = 9

Sale 3: (Dupe)

Sold for 7 keys + ~3-4 keys in items/metal

No outpost link, however: http://puu.sh/oMMeO/72c3055f1d.jpg Same seller is selling it again, for 9 keys. Assuming B/O of 9

Seller: http://backpack.tf/profiles/76561198023542389#!/compare/1462060800/1462147200

Buyer: http://backpack.tf/profiles/76561198090698988#!/compare/1461801600/1462492800

X = 9 (Capped by possible B/O)

Sellers:

9 keys:

http://puu.sh/oMMlV/583090f0f4.png

http://puu.sh/oMMeO/72c3055f1d.jpg

Offers:

http://www.tf2outpost.com/trade/28145204 - 2 days unbumped

http://www.tf2outpost.com/trade/26415558 - 10 months

Sales at:

The value of the three sales represent the UK's emergency number (999)

Going with 9.