Answer:
a = 117°
Step-by-step explanation:
The exterior angle of a triangle = the sum of the remote interior angles.
a + 25° = (a - 47°) + (a - 45°)
a + 25° = (a + a) + (-47 - 45)
a + 25° = 2a - 92°
-2a = -2a
-a +25 = -92
-25 = -25
-a = -117°
a = 117°
