Stress problem

I'm not sure if this is the right forum for this so apologies if not.

I've got a basic (?) stress problem here which I've attached to this post, it's question 8. I know the formula is force/CSA but I'm not getting anywhere near the right answer (0.034N/mm^2).

Could someone give me some help please - this is all very new to me and I'm not sure if any units need changing first. I've worked the CSA out as 100,000mm.


I tried to attach a picture but for some reason it keeps failing - here is the question:

By considering a typical metre length of wall calculate the stress at the base of a 2m tall, 100mm thick, concrete blockwork wall, with a self weight of 17 kN/m^3.