The magnitude j(r) of the current density in a certain cylindrical wire is given as a function of radial distance from the center of the wire's cross section as j(r) = br, where r is in meters, j is in amperes per square meter, and b = 2.35 ✕ 105 a/m3. this function applies out to the wire's radius of 2.00 mm. how much current is contained within the width of a thin ring concentric with the wire if the ring has a radial width of 11.5 μm and is at a radial distance of 1.20 mm?