Urgent:Help!!!

[physicsss]

There is a maximum height of a uniform vertical column made of any material that can support itself without breaking, and it is independent of the cross-sectional area.

(a) Calculate this height for steel (density 7.8 103 kg/m3).

(b) Calculate this height for granite (density 2.7 103 kg/m3).

[Yegor]

You have to know limit of durability of material
M*g=σ*s
M=ρ*l*S
g*l*ρ=σ
l=σ/(g*ρ), where ρ=density, σ=limit of durability (maximal stress), S=Area

[physicsss]

How do I find the limit durability of material?