Sales 1-3:

Sold for $17 (2x) and $13 on marketplace.tf

https://marketplace.tf/items/30024;5;u60

https://manic.tf/keyprice/?at=2018-08-10 - $17 / $1.87 = 9.09 keys

https://manic.tf/keyprice/?at=2018-08-10 - $13 / $1.87 = 6.95 keys

https://manic.tf/keyprice/?at=2018-08-29 - $17 / $1.88 = 9.04 keys

X = 9 (2x)

X = 7

Sale 4:

Sold for 4 keys + ~3 keys in items

Seller: https://backpack.tf/profiles/76561198346729577#!/compare/1539216000/1539475200

Buyer: https://backpack.tf/profiles/76561198077987068#!/compare/1539129600/1539216000

https://backpack.tf/item/2120224201

X = 7

Other Sales:

https://backpack.tf/item/4758254349 (#1-4)

https://backpack.tf/item/2209291290 (#5)

https://backpack.tf/item/2120224201 (#6 & #7)

#1

Untraceable, bought from scrap

https://backpack.tf/profiles/76561198135388328#!/compare/1531958400/1532044800

https://backpack.tf/profiles/76561198263377569#!/compare/1531958400/1532131200

probably went to a private backpack

#2

https://backpack.tf/profiles/76561198263377569#!/compare/1532649600/1532736000

https://backpack.tf/profiles/76561198309332284#!/compare/1532649600/1532736000

#3

Untraceable

https://backpack.tf/profiles/76561198263377569#!/compare/1532649600/1532736000

https://backpack.tf/profiles/76561198309332284#!/compare/1532649600/1532736000

#4

Untraceable

https://backpack.tf/profiles/76561198309332284#!/compare/1533168000/1533254400

https://backpack.tf/profiles/76561198820178900#!/compare/1522540800/1533427200

#5

Untraceable

https://backpack.tf/profiles/76561198311498888#!/compare/1536710400/1536796800

https://backpack.tf/profiles/76561198812539185#!/compare/1536710400/1536796800

7 keys match, but I doubt it sold for only 7.

#6

Untraceable

https://backpack.tf/profiles/76561198337734785#!/compare/1538611200/1538697600

https://backpack.tf/profiles/76561198348661100#!/compare/1537920000/1538784000

Same situation as the one above

#7

Untraceable

https://backpack.tf/profiles/76561198348661100#!/compare/1538784000/1539734400

https://backpack.tf/profiles/76561198346729577#!/compare/1538697600/1539129600

Sellers:

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

https://backpack.tf/item/2120224201 - 15 keys

Sales at:

7 (2x)

9 (2x)

https://i.imgur.com/Zu5VvFY.png - buyers at 7

While there are as many sales at 7 as there are at 9, the buyers appear to be unsuccessful, and both sales at 7 were a fair bit less than the quickbuyers unrounded. Excluding 7.

Going with 9 flat.