Answer:
360°
Explanation:
external angles of a triangle are always equal to 360°
you can also prove this
180-∡9=∡6
180-∡11=∡8
+180-∡10=∡7
540 -(∡9+∡10+∡11)=∡6+∡7+∡8
we know that the sum of the interior angles (∡6, ∡7, ∡8) is equal to 180°
540-(∡9+∡10+∡11)=180
540-180=(∡9+∡10+∡11)
360=∡9+∡10+∡11