Solución
$$\begin{aligned} (2\bold{i}\times 3\bold{j})\times \bold{j} &= 2(\bold{i}\times 3\bold{j})\times\bold{j}\\ &= 2(3)(\bold{i}\times\bold{j})\times\bold{j}\\ &= (6\bold{k})\times\bold{j}\\ &= 6(−\bold{i})=−6\bold{i} \end{aligned}$$