Show that the vectors are not orthogonal with respect to the Euclidean inner product on $R^{2}$, and then find a value of $k$ for which the vectors are orthogonal with respect to the weighted Euclidean inner product $(\mathbf{u}, \mathbf{v})=2 u_{1} v_{1}+k u_{2} v_{2}$.
$$\mathbf{u}=(2,-4), \mathbf{v}=(0,3)$$