Fascinating. Imagine getting Isekai'd only to realize you are not the only one. Sure shield hero had that bit, but there it was established from the start. I'm really curious to see where this goes.
The riddle is easy: melt down the silver and then make three equally sized ignots.
These are medieval coins after all their value is directly tied to the material and not the bank giving you a bit more than the coin material is actually worth (as it is today).