Two forces, $\vec{F}_1 = (2\hat{i} + 3\hat{j})\ \text{N}$ and $\vec{F}_2 = (4\hat{i} - 7\hat{j})\ \text{N}$, act on a body. A third force $\vec{F}_3$ is added so that the body stays in balance. $\vec{F}_3$ is