What is the longitudinal stress induced in the pipe?

Question

A thin walled water pipe carries water a pressure of 2 N/mm² and discharge water into a tank. Diameter of the pipe is 25 mm and thickness is 2.5 mm. What is the longitudinal stress induced in the pipe?

            (a) 0                 (b) 2 N/mm²                (c) 5 N/mm²                 (d) 10 N/mm²