Soil-Water-Plant Relationship

Cumulative infiltration into an agricultural soil is modeled by Kostyakov's equation: $I = 18.0 \cdot t^{0.65}$, where $I$ is cumulative depth in millimeters and $t$ is elapsed time in hours. The instantaneous infiltration rate $i = \frac{dI}{dt}$ at $t = 2.0\text{ hours}$ in millimeters per hour ($\text{mm/h}$) is ________ (round off to two decimal places).