Just for next time you will need to include the compare links showing the items going in and out of both of your inventories.

Item 1:

https://backpack.tf/item/450512829

Sale 1:

https://backpack.tf/profiles/76561198859721638#!/compare/1773532800/1773705600

https://backpack.tf/profiles/76561198834027664#!/compare/1773619200/1773705600

Sold for a Dead Presidents Bot Dogger (8.5) + Nuts n' Bolts Boxcar Bomber (12)

= 20.5

However it caps at Charon's Buy out of 20 keys

https://next.backpack.tf/classifieds/snapshots/Bubbling%20Bonk%20Helm/69b77238df8dc5a13c0046ef

https://imgur.com/a/YOVeAIF

Because both items are outdated (Price of each hasn't had an accepted suggestion within the past 4 months) you will be required to mini each will mean you will need to look at each of the items sales and work out a price.

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Mini For Dead Pres Bot Dogger

Item 1:

https://backpack.tf/item/16493281104

Sale 1:

https://backpack.tf/profiles/76561199072654974#!/compare/1773446400/1773532800

https://backpack.tf/profiles/76561198258287001#!/compare/1772668800/1773532800

Untrace

Sale 2:

https://backpack.tf/profiles/76561198061881189#!/compare/1767225600/1767312000

https://backpack.tf/profiles/76561199072654974#!/compare/1767225600/1767312000

Sold for 6 keys and 14.22 ref (Doesn't seem right though)

No other recent sales for the bot dogger so taking bot buyers:

https://imgur.com/a/ArgDMZo - 8.5

Mini for Nuts & Bolts Boxcar

No other movement for this one except your sale,

Again going with bot buyers

https://imgur.com/a/wYtbIjo - 12

-------------------

Additionally the other movement for the bubbling bonk is bulk which cant be used

https://backpack.tf/profiles/76561198859721638#!/compare/1771718400/1771804800

https://backpack.tf/profiles/76561198025020226#!/compare/1771804800/1771977600

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In short 20 keys works here with the evidence above just for future this is how you would structure it