Two mild steel plates of similar thickness, in butt-joint configuration, are welded by gas tungsten arc welding process using the following welding parameters.
$$\begin{array}{|c|c|} \hline
\text{Welding voltage} & \text{20 V} \\ \hline \text{Welding current} & \text{150 A} \\ \hline \text{Welding speed} & \text{5 mm/s} \\ \hline
\end{array}$$
A filter wire of the same mild steel material having $3$ $\text{mm}$ diameter is used in this welding process. The filler wire feed rate is selected such that the final weld bead is composed of $60\%$ volume of filler and $40\%$ volume of plate material. The heat required to melt the mild steel material is $10$ $J/mm^{3}$. The heat transfer factor is $0.7$ and melting factor is $0.6$. The feed rate of the filler wire is _______________ $\text{mm/s}$ (round off to one decimal place).