Trigonometric levelling was carried out from two stations P and Q to find the reduced level (R. L.) of the top of hillock, as shown in the table. The distance between Stations P and Q is 55 m. Assume Stations P and Q, and the hillock are in the same vertical plane. The R. L. of the top of the hillock (in m) is ____________ (round off to three decimal places).
$$
\begin{array}{|c|c|c|c|}
\hline \text { Station } & \begin{array}{c}
\text { Vertical } \\
\text { angle of } \\
\text { the top of } \\
\text { hillock }
\end{array} & \begin{array}{c}
\text { Staff } \\
\text { reading on } \\
\text { benchmark }
\end{array} & \begin{array}{c}
\text { R.L. of } \\
\text { bench } \\
\text { mark }
\end{array} \\
\hline \mathrm{P} & 18^{\circ} 45^{\prime} & 2.340 \mathrm{~m} & \begin{array}{c}
100.000 \\
\mathrm{~m}
\end{array} \\
\hline \mathrm{Q} & 12^{\circ} 45^{\prime} & 1.660 \mathrm{~m} & \\
\hline
\end{array}
$$