If the vector $\overline{\mathrm{a}}=3\overline{\mathrm{j}}+4\overline{\mathrm{k}}$ is the sum of two vectors $\overline{{\mathrm{a}}_1}$ and $\overline{{\mathrm{a}}_2}$, vector $\overline{{\mathrm{a}}_1}$ is parallel to $\overline{\mathrm{b}}=\overline{\mathrm{i}}+\overline{\mathrm{j}}$ and vector $\overline{{\mathrm{a}}_2}$ is perpendicular to $\overline{\mathrm{b},}$ then $\overline{{\mathrm{a}}_1}$=