$\begin{align}  & 68{}^\circ +x=2x\text{   }\!\!\{\!\!\text{  Sum of two opp}\text{. }\angle \text{s in a }\vartriangle =\text{opp}\,\text{ ext}\text{. }\angle \text{ }\!\!\}\!\!\text{ }----(i) \\ & x=68{}^\circ  \\ & 2x+m=180{}^\circ \text{    }\!\!\{\!\!\text{  sum of angles on straight line }\!\!\}\!\!\text{ }----(ii) \\ & 2(68{}^\circ )+m=180{}^\circ  \\ & m=44{}^\circ  \\\end{align}$