Hydrology and Runoff

Using Kirpich's formula $t_c = 0.0195 L^{0.77} S^{-0.385}$ (where $L$ is in meters and $S$ is dimensionless slope), for a watershed flow path length $L = 1000\text{ m}$ on slope $S = 0.04$, given $1000^{0.77} \approx 204.17$ and $0.04^{-0.385} \approx 3.46$, the time of concentration $t_c$ in minutes is: