That's a lot of banter!
Remember - the boat's guard wanted to know what money was in smuggler's banter.
Right-click the paper in your inventory to get a good look at it.
The symbols on the left of the equations represent the thing you'd say - the symbols on the right side of the equations represent the thing you'd mean.
In smuggler's banter, you'd say one thing, but mean another.
Of course - in the "feather = key" drawing, you'd say something like "Throw me the feather!" to mean "Throw me the key!"
We're talking about money, so look for coins.
It wouldn't hurt to scan the rest of the paper for anything useful - the third question was about wine, after all, and you learned what Harm liked to drink in these hints.
Favourite animal - ? Favourite wine - ?
A silver tongue goes a long way - we've finally earned an audience with Harm himself.