Let $\overline{\mathrm{a}} = 4\overline{\mathrm{i}}- 3\overline{ \mathrm{j}} + 5\overline{\mathrm{k}}.$ A vector $\overline{\mathrm{b}}$ is coplanar with $\overline{\mathrm{i}} , \overline{\mathrm{j}}$ and orthogonal to $\overline{a}$ and has magnitude $\left|\overline{\mathrm{a}}\right|,$ then $\overline{\mathrm{b}}$ is