Let a,b,c are three non-coplanar vectors such that
$\begin{array}{l}\overline{{\mathrm{r}}_1}=\overline{\mathrm{a}}-\overline{\mathrm{b}}+\overline{\mathrm{c}},{\mathrm{r}}_2=\overline{\mathrm{b}}+\overline{\mathrm{c}}-\overline{\mathrm{a}},{\mathrm{r}}_3=\overline{\mathrm{c}}+\overline{\mathrm{a}}+\overline{\mathrm{b}},\\ \mathrm{r}=2\overline{\mathrm{a}}-3\overline{\mathrm{b}}+4\overline{\mathrm{c}},\text{ If }\overline{\mathrm{r}}={\mathrm{\lambda }}_1\overline{{\mathrm{r}}_1}+{\mathrm{\lambda }}_2\overline{{\mathrm{r}}_2}+{\mathrm{\lambda }}_3\overline{{\mathrm{r}}_3},\text{ and }{\mathrm{\lambda }}_1+{\mathrm{\lambda }}_2+{\mathrm{\lambda }}_3=\mathrm{k}\end{array}$
the, the value of k is