Vector Algebra: JEE Main 2020 Mathematics question

Let $\overrightarrow a = \widehat i - 2\widehat j + \widehat k$ and $\overrightarrow b = \widehat i - \widehat j + \widehat k$ be two vectors. If $\overrightarrow c$ is a vector such that $\overrightarrow b \times \overrightarrow c = \overrightarrow b \times \overrightarrow a$ and $\overrightarrow c .\overrightarrow a = 0$, then $\overrightarrow c .\overrightarrow b$ is equal to