Calculating the Young modulus

http://www.flickr.com/photos/51956290@N0…
So normally:

E = Stress/strain
Stress = f/a
Strain = >x/x

So can someone please explain to me how the >x would rearrange to Fx/AE? The option I originally picked was C.

I can't seem to make it rearrange to this at all! It's also multiple choice so the mark scheme has no working out.

Thanks for any help

E=Stress/Strain, Stress=f/a, Strain =(Change in x)/x
E=(f/a)/((Change in x)/x)which rearranges to E=f*x/a*(Change in x)
Hence, Change in x=f*x/a*E