A cylindrical shell of radius 7cm and length 2.4 cm has charge uniformly distributed on its surface. The magnitude of the electric field at a point 19 cm radically outward from its axis, at the midpoint of the shell, is 36kN/C. Find:
a) The net charge on the shell
b) The electric field at a point 4cm radically outward from its axis, at the midpoint of the shell.