b) give reasons for your answer

Answer:
80° is the correct answer
Step-by-step explanation:
The angle B is 100° because of the property of the vertically opposite angle.
As we know the property consecutive interior angle that the sum of two angle is 180°
So
Angle B + Angle X =180°
100 °+ Angle X =180°
Angle X=180°-100°
Angle X = 80°