Textbook Problem

A built-up shape consisting of two $\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$4$}\right.\times 18$ flanges and a $\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$4$}\right.\times 52$ web is used as a beam. If A572 Grade 50 steel is used, what is the nominal flexural strength based on flange local buckling? For width-thickness ratio limits for welded shapes, refer to Table B4.1b in Chapter B of the AISC Specification, “Design Requirements?