I’d like to ask the good people of this community that, if you do know the solution or figure it out, that you not share the answer here. Feel free to announce your success, but there’s something to be said for discovering the answer completely unaided, even if it takes years.
It’s embarrassingly obvious once you see it though.
You solve for it.
If the answer you get is right, you’ll be able to apply it to every trio and get the number on the “line”. It’s kinda like how you can plug in your answer into a quadratic equation to double check you got it right.