A rod of length L= 500 mm and cross sectional area A = 60 $$mm^{2}$$ is made of an elasto plastic material having a modular of elasticity E = 200 Gpa nits elastic range and yield point $$\sigma y$$=300 Mpa. The rod is subjected to an axial load until it is stretched 7 mm and the load is then removed. What is the resulting permanent set?

A

6.25 mm

B

6.50 mm

C

6.00 mm

D

5.95 mm