Let a =2 i -3 j +4 k and b =7 i + j -6 k. If r × a = r × b, r ·( i +2 j + k )=-3, then r ·(2 i -3 j + k ) is equal to:

Let $\displaystyle \overrightarrow{\mathrm{a}}=2 \hat{i}-3 \hat{j}+4 \hat{k}$ and $\displaystyle \overrightarrow{\mathrm{b}}=7 \hat{i}+\hat{j}-6 \hat{k}$.If $\displaystyle \overrightarrow{\mathbf{r}} \times \overrightarrow{\mathbf{a}}=\overrightarrow{\mathbf{r}} \times \overrightarrow{\mathbf{b}}, \overrightarrow{\mathbf{r}} \cdot(\hat{i}+2 \hat{j}+\hat{k})=-3$, then $\displaystyle \overrightarrow{\mathbf{r}} \cdot(2 \hat{i}-3 \hat{j}+\hat{k})$ is equal to :