A long, solid cylindrical wire of radius \(R\) carries current directed parallel to its central axis. The current density within the wire is non-uniform and depends on the radial distance \(r\) from the central axis according to \(J(r) = C r^2\), where \(C\) is a positive constant. Which of the following integral expressions represents a correct setup using Ampère's law to determine the magnitude of the magnetic field \(B(r)\) at a distance \(r < R\) from the central axis?