Subtract the interior angles from 180° to find the exterior angles. For the exterior angle at A, 180 – 80 = 100°. For the exterior angle at B, 180 – 85 = 95°.

Co-interior angles add up to 180°. The lines make a C shape which can also be back to front. Next page. Missing angles question. Previous page. Vertically opposite angles. More guides on this topic.