The hyetograph in the figure corresponds to a rainfall event of $\text{3 cm}$.
![](https://civil.gateoverflow.in/?qa=blob&qa_blobid=11528657035856458159)
If the rainfall event has produced a direct runoff of $\text{1.6 cm}$, the $\phi$-index of the event (in $\text{mm/hour},\textit{round off to one decimal place}$) would be