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 intensity of storm II (in cm/h) is

1. $2.00$
2. $1.75$
3. $1.50$
4. $2.25$