Infiltration, Evaporation & Hydrologic Losses

The infiltration capacity of a watershed follows Horton's equation: $f_t = f_c + (f_0 - f_c) e^{-k t}$. Given initial infiltration capacity $f_0 = 40\text{ mm/h}$, final steady capacity $f_c = 10\text{ mm/h}$, and decay constant $k = 0.5\text{ h}^{-1}$, the infiltration capacity at time $t = 2\text{ h}$ is ________ $\text{mm/h}$ (round off to two decimal places).