$11-49.$ The beam is made in the shape of a frustum that has a diameter of $0\mathrm{.}3$ m at $\backslash ($ A $\backslash )$ and a diameter of $0\mathrm{.}6$ m at $\backslash ($ B $\backslash ).$ If it supports a couple moment of $\backslash (12\backslash$mathrm$\{$kN$\}\backslash$cdot $\backslash$mathrm$\{$m$\}\backslash )$ at its end, determine the absolute maximum bending stress in the beam and specify its location $\backslash ($ x $\backslash ).$