$\begin{align}   & \overset{\vartriangle }{\mathop{OMH}}\,:\widehat{M}=180-\left( \overset{119}{\mathop{\not{90+29}}}\, \right)=61{}^\circ  \\  & \overset{\vartriangle }{\mathop{OHN}}\,:\widehat{N}=180-\left( \overset{143}{\mathop{\not{90+53}}}\, \right)=37{}^\circ  \\  & \widehat{M}-\widehat{N}=61-37=24{}^\circ  \\ \end{align}$