The two vectors $(\vec a = 2\hat i+\hat j+3\hat k,\,\vec b = 4\hat i-λ\hat j+6\hat k)$ are parallel if $λ$ is equal to:

2 -3 3 -2

-2

$\vec a ||\vec b⇒\vec a=k\vec b$ $\frac{2}{4}=\frac{1}{-λ}=\frac{3}{6}$ $λ=-2$