A rigid massless bar $\text{PQR}$ is hinged at its end $\text{P}$ and supported through a spring of stiffness $k$ at point $\text{Q}$. A vertically downward force $W=560 \mathrm{~N}$ is applied at the free end $\text{R}$ of the bar. If the vertical component of the displacement at $\text{R}$ is $30$ mm , then the stiffness of the spring $\text{(in $\mathrm{kN} / \mathrm{m}$, rounded off to one decimal place)}$ is _____________.
