working stress

[operator]

I need help with a question. A material to be used for a piston rod has an ultimate strength of 414 000 kPa. The maximum load on the piston is to be 70 000 N and the safety factor for the rod is 12. Calculate the working stress of the piston rod and the diameter of the piston rod? How do i begin. I know that Stress = load divided by area, but how do I find the area when i don't know the size of the material? What am i missing? That's all the information I have. Thx

[Dave]

(Moved to classical mechanics because it's a better home for the thread)