\[Рисунок\ в\ учебнике.\]
\[\cup AB = 74{^\circ};\angle ABC = 68{^\circ}:\]
\[\cup AC = 2\angle ABC = 136{^\circ};\]
\[\cup AB + \cup BC + \cup AC = 360{^\circ}\]
\[74{^\circ} + \cup BC + 136{^\circ} = 360{^\circ}\]
\[\cup BC = 150{^\circ}.\]
\[Ответ:\ \ 150{^\circ}.\]