An unconfined aquifer of areal extent $20 \mathrm{~km} \times 20 \mathrm{~km}$ has hydraulic conductivity of $4 \mathrm{~m} / \mathrm{day}$, porosity of $0.32$, and storage coefficient (specific yield) of $0.18$. If the initial saturated thickness of the aquifer is $30 \: \mathrm{m}$ , and $4 \times 10^{8} \mathrm{~m}^{3}$ of water is extracted from the aquifer, then the decline in the saturated thickness is $\_\_\_\_\_\_$ m. (rounded off to two decimal places)
