Solve this following

Let $\overrightarrow{\mathrm{u}}$ be a vector coplanar with the vectors $\overrightarrow{\mathrm{a}}=2 \hat{\mathrm{i}}+3 \hat{\mathrm{j}}-\hat{\mathrm{k}}$ and $\overrightarrow{\mathrm{b}}=\hat{\mathrm{j}}+\hat{\mathrm{k}}$. If $\overrightarrow{\mathrm{u}}$ is perpendicular

to $\overrightarrow{\mathrm{a}}$ and $\overrightarrow{\mathrm{u}} \cdot \overrightarrow{\mathrm{b}}=24$, then $|\overrightarrow{\mathrm{u}}|^{2}$ is equal to-