$\mathbf{r}_{AB} = 0.2 \mathbf{i} + 0.1 \mathbf{j}$ $\mathbf{F} = 100 \mathbf{i} + 0 \mathbf{j} + 0 \mathbf{k}$ (Assuming F is along the x-axis)
$\mathbf{M}_A = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \ 0.2 & 0.1 & 0 \ 100 & 0 & 0 \end{vmatrix} = 0 \mathbf{i} + 0 \mathbf{j} -10 \mathbf{k}$ $\mathbf{r}_{AB} = 0
However, without specific values of external forces and distances, a numerical solution is not feasible here. $\mathbf{r}_{AB} = 0