$.$ Suppose the rainfall is $145$ cm$/$year of which $50\%$ percolates into the ground

while the rest is runoff. A farmer irrigates crops using well water. Of the extracted

well water, $80\%$ is lost by evapotranspiration, the rest percolates back into the

ground. How much groundwater could a farmer on a $20,000$ hectares $(2\backslash$times $108$ m$2$

$)$

farm extract from the ground per year, without depleting the groundwater

reservoir volume?