Eh... I don't like this suggestion.

Sale 1

[No OP Trade] Sold with KS Pan for Bubbling Ballcap

Cone had no trade, presuming offered

B/O for Ballcap was 22 keys (1.45)

X + 8.2 = 22 keys

X = 14 keys

Pan http://backpack.tf/item/552496288

Cone http://backpack.tf/item/767769122

Ballcap http://backpack.tf/item/1944866534

Mini for Pan

http://steamcommunity.com/market/listings/440/Strange%20Killstreak%20Frying%20Pan Sold for $20.67 on Nov 14th

20.67 + 20.67/1.15 = 38.64

38.64/2 = $19.32

Keys were $2.35 on Nov 14th

19.32/2.35 = 8.2 keys

Sale 2 QUICKSELL

http://www.tf2outpost.com/trade/23997867 QuickSold for a White Horace

X = 11*0.9

X = 10

Horace http://backpack.tf/item/2999785679

Dead Cone http://backpack.tf/item/458605034

Sale 3

[No OP Trade] Sold with 2 keys pure for Stormy Nano

X + 2 = 19

X = 17

Nano http://backpack.tf/item/1007064870

Cone http://backpack.tf/item/458605034

Mini for Nano

Seller for 19 keys on classifieds, using 19