The infiltration rate $f$ in a basin under ponding condition is given by $f=30+10 e^{-2 t}$, where, $f$ is in $\mathrm{mm} / \mathrm{h}$ and $t$ is time in hour. Total depth of infiltration (in $\mathrm{mm},$ up to one decimal place) during the last 20 minutes of a storm of 30 minutes duration is

The infiltration rate $f$ in a basin under ponding condition is given by $f=30+10 e^{-2 t}$, where, $f$ is in $\mathrm{mm} / \mathrm{h}$ and $t$ is time in hour. Total depth of infiltration (in $\mathrm{mm},$ up to one decimal place) during the last 20 minutes of a storm of 30 minutes duration is

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