Please, show a picture.
(for better understanding)
Another solution
- Take a point $\displaystyle E$ on the extension of $\displaystyle \overline{AC}$ such that $\displaystyle \overline{BA}=\overline{BE}\implies\measuredangle~ CBE=x~\therefore~\triangle{BAC}\cong\triangle{BED}$.
- Finally $\displaystyle \measuredangle~BDE=4x\implies{x}=18^\circ~\blacksq uare$