Trying again, new sale just a few hours ago.

Sale 1:

https://marketplace.tf/items/tf2/31038;5;u127

https://backpack.tf/item/8157309683

May 15th, 2020: $35.00

Keys were $1.91 that day, so 35 / 1.91 = 18.32, rounding to 18 keys.

Sale 2:

https://marketplace.tf/items/tf2/31038;5;u127

https://backpack.tf/item/8166831848 - Probably this one?

June 18th, 2020: $39.99

Keys were, or well are, $1.97~$1.98 on that day, SO 39.99 / 1.98 = 20.2, rounding to 20 keys.

(Fine with not waiting for the day to close for mp key prices, since we round here anyways. It'd take a 3 or 4 cent drop in key prices for this to not still be a valid rounding.)

Taking 18-20 keys.