The value of d is 80°.
Solution:
The image of the question is attached below.
Given is a cyclic quadrilateral.
To find the value of d:
In a cyclic quadrilateral, the opposite angles are supplementary.
⇒ 100° + d = 180°
Subtract 100° from both sides of the equation.
⇒ 100° + d – 100° = 180° – 100°
Combine like terms together.
⇒ 100° – 100° + d = 180° – 100°
⇒ 0 + d = 80°
⇒ d = 80°
Option D: 80° is the correct answer.
Hence the value of d is 80°.