An infinitely long conducting cylindrical rod with a positive charge lambda per unit length is surrounded by a conducting cylindrical shell (which is...

An infinitely long conducting cylindrical rod with a positive charge lambda per unit length is surrounded by a conducting cylindrical shell (which is also infinitely long) with a charge per unit length of -2 lambda and radius r_1, as shown in the figure.What is sigma_inner, the surface charge density (charge per unit area) on the inner surface of the conducting shell?