X
( = [?]
DK
x Х
А AK
140°
B
HC
Angles are not drawn to scale

Answer:
40 degrees
Step-by-step explanation:
Supplementary angles are a pair of angles that add up to 180 degrees
Since ABD and DBC are supplementary, you can make the equation:
180=140+x
Simplify and you get x=40
[tex]\bf \large \implies \: \: x \: + \: 140 \degree \: = \: 180 \degree[/tex]
[tex]\bf \large \implies \: \: x \: = \: 180 \degree - \: 140 \degree[/tex]
[tex]\bf \large \implies \: \: x \: = \: 40 \degree[/tex]