Let a =- i + j and b = i + j - k be two given vectors. If a vector c satisfies ( a × c )+ b = 0 and a · c =3, then 10| c |^2 is equal to \ \ \ \.

Let $\displaystyle \vec{a}=-\hat{i}+\hat{j}$ and $\displaystyle \vec{b}=\hat{i}+\hat{j}-\hat{k}$ be two given vectors. If a vector $\displaystyle \vec{c}$ satisfies $\displaystyle (\vec{a} \times \vec{c})+\vec{b}=\overrightarrow{0}$ and $\displaystyle \vec{a} \cdot \vec{c}=3$, then $\displaystyle 10|\vec{c}|^2$ is equal to \_\_\_\_.