Daily reference evapotranspiration ($ET_0$) is estimated using the Hargreaves-Samani temperature-radiation equation: $ET_0 = 0.0023 \cdot R_a \cdot (T_{\text{mean}} + 17.8) \cdot (T_{\text{max}} - T_{\text{min}})^{0.5}$, where $R_a$ is extraterrestrial solar radiation expressed in equivalent water evaporation depth of $15.0\text{ mm/day}$. For a sunny summer day with recorded temperatures of $T_{\text{max}} = 34.0^\circ\text{C}$, $T_{\text{min}} = 18.0^\circ\text{C}$, and $T_{\text{mean}} = 26.0^\circ\text{C}$, the estimated reference evapotranspiration $ET_0$ in $\text{mm/day}$ is ________ (round off to two decimal places).