We will use Congruent supplements theorem, which states If 2 angles are supplementary to the same angle, then they are congruent to each other.
Since, angles FBC and CBG are supplements to each other.
So,

Angles DBG and DBF are supplements to each other.
So,

And angles CBG and DBF are supplements to each other.
So,

By using these congruent conditions, we conclude that angles FBC and DBG are congruent to each other.
Therefore,
