A constant torque acting on a uniform circular wheel changes its angular momentum form $A_0$ to $4A_0$ in $4 \text{second}$, the magnitude of this torque is

A force $\overrightarrow{F}=2\hat{\mathrm{i}}-3\hat{\mathrm{k}}$ acts on a particle at $\overrightarrow{r}=0.5\hat{\mathrm{j}}-2\hat{\mathrm{k}}$. The torque $\overrightarrow{\tau }$ acting on the particle relative to a point with coordinates $\left(2.0 \mathrm{m}, 0, –3.0 \mathrm{m}\right)$ is: