A tacheometer was placed at point $P$ to estimate the horizontal distances $PQ$ and $PR$. The corresponding stadia intercepts with the telescope kept horizontal, are $0.320$ m and $0.210$ m, respectively. The $\angle QPR $ is measured to be $61^{\circ} 30’ 30’’$. If the stadia multiplication constant $=100$ and stadia addition constant $=0.10$ m, the horizontal distance (in m) between the points $Q$ and $R$ is __________