Use the note that Linear pairs have sum 180°
[tex]\\ \rm\rightarrowtail m\overset{\frown}{CD}+122=180[/tex]
[tex]\\ \rm\rightarrowtail m\overset{\frown}{CD}=180-122=58°[/tex]
Now
- A whole angle is 360° or 2π
[tex]\\ \rm\rightarrowtail x+122+58+90=360[/tex]
[tex]\\ \rm\rightarrowtail x+270=360[/tex]
[tex]\\ \rm\rightarrowtail m\overset{\frown}{DB}=90°[/tex]
