the sum of the interior angles of a triangle is equal to 180, therefore:
7x + 30 + y = 180
Where y = Missing angle
Solving for y:
y = 180 - 30 - 7x
y = 150 - 7x
The missing angle y and the angle 10x are supplementary angles, this means:
10x + y = 180
Replacing the value of y:
10x + 150 - 7x = 180
3x + 150 = 180
Solving for x:
3x = 180 - 150
3x = 30
x = 30/3
x = 10
Since the exterior angle is 10x:
the measurement is :
10(10) = 100