the hoop stress developed at the inner radius is

Question

A thick cylinder is subjected to internal pressure of 100 N/mm². If hoop stress developed at the outer radius of the cylinder is 100N/mm², the hoop stress developed at the inner radius is           

         (a) 100 N/mm²                  (b) 200 N/mm²        

         (c) 300 N/mm²                 (d) 400 N/mm²