At a station, Storm I of $5$ hour duration with intensity $2$ cm/h resulted in a runoff of $4$ cm and Storm II of $8$ hour duration resulted in a runoff of $8.4$ cm. Assume that the $\phi$ – index is the same for the both the storms. The $\phi$ – index (in cm/h) is
- $1.2$
- $1.0$
- $1.6$
- $1.4$