Let a = i -2 j +3 k, b = i + j + k and c be a vector such that a +( b × c )= 0 and b · c =5. Then, the value of 3( c · a ) is equal to \ \ \ \.

Let $\displaystyle \vec{a}=\hat{i}-2 \hat{j}+3 \hat{k}, \vec{b}=\hat{i}+\hat{j}+\hat{k}$ and $\displaystyle \vec{c}$ be a vector such that $\displaystyle \vec{a}+(\vec{b} \times \vec{c})=\overrightarrow{0}$ and $\displaystyle \vec{b} \cdot \vec{c}=5$. Then, the value of $\displaystyle 3(\vec{c} \cdot \vec{a})$ is equal to \_\_\_\_.