Answer:
140°
Step-by-step explanation:
[tex] \because m\widehat{BG} = 360\degree - m\widehat{GCB} \\
\therefore m\widehat{BG} = 360\degree - 300\degree \\
\therefore m\widehat{BG} = 60\degree \\
\because m\widehat{BGD} = m\widehat{BG}
+m\widehat{GD}\\
\therefore m\widehat{BGD} = 80\degree+60\degree\\
\therefore m\widehat{BGD} = 140\degree\\
\because m\angle BAD = m\widehat{BGD} \\
\huge\purple {\boxed {\therefore m\angle BAD =140\degree}} [/tex]
