A truss $\text{EFGH}$ is shown in the figure, in which all the members have the same axial rigidity $\text{R}$. In the figure, $\text{P}$ is the magnitude of external horizontal forces acting at joints $\text{F}$ and $\text{G}$.
If $R=500 \times $ $10^{3}$ $\text{kN}$, $P=150$ $\text{kN}$ and $\text{L=3 m}$, the magnitude of the horizontal displacement of joint $\text{G}$ (in $\text{mm}, \textit{round off to one decimal place}$) is _____________________