The position vector of 1   kg object is r → = 3 i ^ - j ^   m and its velocity v → = 3…

Angular momentum of a particle is given by,

$\overrightarrow{L}=\overrightarrow{r}\times \overrightarrow{P}=\overrightarrow{r}\times m\overrightarrow{v}$ also $m=1 \mathrm{kg}$.

$\Rightarrow \overrightarrow{L}=\left(3\hat{\mathrm{i}}-\hat{\mathrm{j}}\right)\times \left(3\hat{\mathrm{j}}+\hat{\mathrm{k}}\right)=\left(9\hat{\mathrm{k}}-3\hat{\mathrm{j}}-\hat{\mathrm{i}}\right) \mathrm{N} \mathrm{m} \mathrm{s}$

The magnitude of the angular momentum will be,

$\Rightarrow \left|\overrightarrow{L}\right|=\sqrt{9^2+3^2+1^2}=\sqrt{91} \mathrm{N} \mathrm{m} \mathrm{s}$

Therefore, the value of $x=91$.