Answer:
77*
First we are going to take our given number, 25* and 78* and add them together.
25* + 78* = 103*
And subtract our answer, 103*, from 180*.
180* - 103* = 77*
77* is our missing angle. To prove it, we add angle measures a, b, and c, to make the number 180*
25* + 78* + 77* = 180*
Another way to write it is . . .
180* - (A + B) = C
~Hope this helps~
