The rigid-jointed plane frame QRS shown in the figure is subjected to a load $P$ at the joint $R$. Let the axial deformations in the frame be neglected. If the support $S$ undergoes a settlement of $\Delta = \frac{PL^3}{\beta EI}$, the vertical reaction at the support $S$ will become zero when $\beta$ is equal to
- $0.1$
- $3.0$
- $7.5$
- $48.0$