Two 0.075- by 0.075-m equal leg angles, positioned with the legs 0.025 m apart...

Two 0.075- by 0.075-m equal leg angles, positioned with the legs 0.025 m apart back to back, as shown in Fig. P11.22, are used as a column. The angles are made of structural steel with 203 MPa and E = 210 GPa.The area properties of an angle are thickness t = 0.0125 m, A = 1.719 x 10^-3 m², and I_c = 8.6 x 10^-7 m⁴, I/c = S = 1.719 x 10^-5 m³, r_c = 0.0225 m, and Assume that the columns are connected by lacing bars that cause them to act as a unit. Determine the critical stress of the column by using the AISC formula, Eq. (11.13), for effective column lengths (a) 2.1 m and (b) 4.2 m.