Vector Algebra: JEE Main 2019 Mathematics question

Let $\overrightarrow a$ = $\widehat i - \widehat j$, $\overrightarrow b$ = $\widehat i + \widehat j + \widehat k$ and $\overrightarrow c$ be a vector such that $\overrightarrow a$ × $\overrightarrow c$ + $\overrightarrow b$ = $\overrightarrow 0$ and $\overrightarrow a$ . $\overrightarrow c$ = 4, then |$\overrightarrow c$|² is equal to :