I was unclear. When I say $X I don't mean a flat amount per fare. (You are correct in that regard.) I mean an agreed upon payment formula of $y * miles + $z * m

I was unclear. When I say $X I don't mean a flat amount per fare. (You are correct in that regard.) I mean an agreed upon payment formula of $y * miles + $z * miles = $X. That formula is not secret. And does not contain $fare as a variable.