Determine the axial strain in the cylindrical wall at the mid depth, when the Young's modulus and the Poisson's ratio of the container material is 200 GPa and 0.6 respectively. The axial and the circumferential stress are equal and its value is 20 MPa.

A

$$2kshI0^{-5}$$

B

$$6kshI0^{-5}$$

C

$$7kshI0^{-5}$$

D

$$4kshI0^{-5}$$