. A very long straight conductor has a circular cross-section of radius R and carries a current density J

Inside the conductor there is a cylindrical hole of radius a = R/4 whose axis is parallel to the axis of the conductor and a distance b = R/2 from it. Let the z-axis be the axis of the conductor, and let the axis of the hole be at x = b. The magnetic field at x = 2r on the x-axis will be