Recall that the sum of angles on a straight line is 180 degrees.
Therefore, for the line AC, it can be deduced that:
[tex]m\angle ABD+m\angle CBD=180\degree[/tex]
The question provides the following angle measure:
[tex]m\angle CBD=140\degree[/tex]
Substituting the angle measure into the formula, the unknown angle can be solved as follows:
[tex]\begin{gathered} m\angle ABD+140\degree=180\degree \\ m\angle ABD=180\degree-140\degree \\ m\angle ABD=40\degree \end{gathered}[/tex]
ANSWER
[tex]\begin{equation*} m\angle ABD=40\degree \end{equation*}[/tex]
