Answer:
360°
Step-by-step explanation:
We need only remember that the sum of the measures of the interior angles of a triangle is 180°. Angle c and 112° form a pair of "straight angles," so they add up to 180°; as a consequence, Angle c = 180° - 112°, or 68°.
With two of the interior angles now known, we can calculate the third, Angle A: It is 180° less (51° + 68°), or 180° - 119°, or 61°.
That means that the measure of Angle B is 180° - 61° = 119°
Looking at the pair C and 112°, we identify the exterior angle as 112°.
Looking at the pair A and B, or 61° and 119°, we identify the exterior angle as 119°.
Finally, looking at the pair 51° and (180° - 51°), or
51° and 129°, we identify the exterior angle as 129°.
Then the sum of the exterior angles 129° and 119° and 112° is 360°.
