Vectors in Space · Challenge problem

Vectors satisfy $\lVert \mathbf u \rVert = 3$, $\lVert \mathbf v \rVert = 4$ and $\mathbf u \cdot \mathbf v = 6$. Find $\lVert (2\mathbf u - \mathbf v) \times (\mathbf u + 3\mathbf v) \rVert$.