Find the value of x when angle a is 90°, angle b is 40°, and angle c is x+57.

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