Respuesta :

The sum of the all angles are 180.

Then,  a + b + c =  180.

Given, a =  90, b = 40 and c = x + 57.

90 + 40 + c =  180.

130 + c = 180

c = 180 - 130

c = 50

Now plug in the value for c and then solve for x.

c = x + 57

50 =x + 57

50 - 57=x

-7 = x

x = -7

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