The torque of a force  $\mathbf{F}=2\hat{i}-3\hat{j}+5\hat{k}$  acting at a point whose position vector  $\mathbf{r}=3\hat{i}-3\hat{j}+5\hat{k}$  about the origin is 

We know that, torque, $\tau =\mathbf{r}\times \mathbf{F}$

Given,  $\mathbf{F}=2\hat{i}-3\hat{j}+5\hat{k}$

$\Rightarrow \mathbf{r}=3\hat{i}-3\hat{j}+5\hat{k}$

Now,   $\tau =\left|\begin{array}{ccc}\hat{i}& \hat{j}& \hat{k}\\ 3& -3& 5\\ 2& -3& 5\end{array}\right|$

$\tau =(-15+15) \widehat{i }-(15-10)\widehat{ j }(-9+6)\hat{k}$

$\tau =0-5\hat{j}-3\hat{k}$

$\Rightarrow \tau =-5\hat{j}-3\hat{k}$