The position vector of 1 kg object is $\overrightarrow r = \left( {3\widehat i - \widehat j} \right)m$ and its velocity $\overrightarrow v = \left( {3\widehat j + \widehat k} \right)m{s^{ - 1}}$. The magnitude of its angular momentum is $\sqrt x $ Nm where x is ___________.