Respuesta :

mhanifa

Answer:

d. 63

Step-by-step explanation:

sum of 3 interior angles= 180°

78°+39°+a=180°

a= 180°- 117°

a= 63°

allyvdaigle

Answer:

D. 63°

Step-by-step explanation:

The Triangle Sum Theorem says that all of the angles in a triangle add up to 180°.

78° + 39° = 117°. Think of it like algebra. 180° - 117° = 63°. I hope this helps :)

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