An infinitely long, cylindrical, insulating shell of inner radius a and outer radius b has a uniform volume charge density ?. A line of uniform linear charge density ? is placed along the axis of the shell. Determine the electric field in the following regions. (Choose a gaussian cylinder of radius r and length L. Use any variable or symbol stated above along with the following as necessary: ke.) (a) r < a magnitude E = direction (b) a < r < b magnitude E = direction (c) r > b magnitude E = direction