Let  $\overrightarrow{\mathrm{a}}=-\hat{\mathrm{i}}-\hat{\mathrm{k}},\overrightarrow{\mathrm{b}}=-\hat{\mathrm{i}}+\hat{\mathrm{j}}\mathrm{and}\overrightarrow{\mathrm{c}}=\hat{\mathrm{i}}+2\hat{\mathrm{j}}+3\hat{\mathrm{k}}$ be three given vectors. If $\overrightarrow{\mathrm{r}}$ is a vector such that  $\overrightarrow{\mathrm{r}}\times \overrightarrow{\mathrm{b}}=\overrightarrow{\mathrm{c}}\times \overrightarrow{\mathrm{b}}\mathrm{and}\overrightarrow{\mathrm{r}}\mathrm{·}\overrightarrow{\mathrm{a}}=0$, then the value of $\overrightarrow{\mathrm{r}}\mathrm{·}\overrightarrow{\mathrm{b}}$, is