Answer:
The interior and exterior angles total 180
3
x
+
(
x+
20
)
=
180
4
x
+
20
=
180
4
x
=
160
x
=
40
So the interior angle is 120 and the exterior is 60
360 divided by the exterior angle = number of sides
360
60
=6
6 sides,
6
×
120
=720 in total
720
180
=4
4 triangles