Linear Expansion

[benzimm86]

a copper cylinder(3 cm long) and a brass cylinder(5 cm long) are stacked end to end. each cylinder has a radius of .25 cm a compressive force of f=6500 N is applied to the right end of the brass where the other copper end is against a sollid object. find the amount by which the length of the stack decreases

[benzimm86]

with brass being 9.0*10^10 and copper being 1.1*10^11 what i came up with was 5 cm (for the total length of the copper piece plus the brass piece) 3250 being half of the compression force and 9.9*10^21 for the brass and the copper

my equation is (5*3250)/(9.9*10^21)=1.6*10^-18