If $\overline{\mathrm{a}},\overline{\mathrm{b}},\overline{\mathrm{c}}$ are three non - coplanar vectors represented by concurrent edges of a parallelopiped of volume 4 cu. units then $\left(\overline{\mathrm{a}}+\overline{\mathrm{b}}\right).\left(\overline{\mathrm{b}}\times \overline{\mathrm{c}}\right)+\left(\overline{\mathrm{b}}+\overline{\mathrm{c}}\right).\left(\overline{\mathrm{c}}\times \overline{\mathrm{a}}\right)+\left(\overline{\mathrm{c}}+\overline{\mathrm{a}}\right).\left(\overline{\mathrm{a}}\times \overline{\mathrm{b}}\right)=$