Find the value of $k$ for which the line $kx + 3y = 6$ is parallel to the line $2x - y = 4$.

The line $2x - y = 4$ has gradient $2$. Rearranging $kx + 3y = 6$ gives $y = -\dfrac{k}{3}x + 2$, with gradient $-\dfrac{k}{3}$. Parallel lines have equal gradients, so $-\dfrac{k}{3} = 2$ and $k = -6$. Dropping the negative sign gives $k = 6$, which makes the lines meet.