The design оf а white оаk [E = 12.1 GPа, σPL = 24 MPa] cоlumn of square cross section has the following requirements. It must be 9.0 m long, it must have pinned ends, and it must support an axial load of 70 kN with a factor of safety of 5.0 against buckling. Determine the required width of the cross section.