The velocity field of an incompressible flow in a Cartesian system is represented by

$$\overrightarrow{V}=2\left ( x^{2}-y^{2} \right )\widehat{i}+v\widehat{j}+3\widehat{k}$$

Which one of the following expressions for $v$ is valid?

1. $-4xz + 6xy$
2. $– 4xy – 4xz$
3. $4xz – 6xy$
4. $4xy + 4xz$