$\backslash$table$[[,$PROBLEM $3],[\backslash$table$[[($a$)$ Knowing that ${}_{\text{a}\text{l}\text{l}}=24$ksi and ${}_{\text{a}\text{l}\text{l}}=14\mathrm{.}5$ksi select the$],[$most economical wide$-$flange shape that should be used to$],[$support the loading shown. $(b)$ Determine the values to be$],[$expected for ${}_m,{}_m,$ and the principal stress ${}_{\text{m}\text{a}\text{x}}$ at the$],[$junction of a flange and the web of the selected beam.$]],]]$