A water table thickness in unconfined aquifer is 36m. An extraction well supplies water to a city from this aquifer at the rate of 1000m3/d. An observation well placed at the distance of 80m 15orthwest shows a drawdown of 0.5m. Another observation well located at 120m southeast from the center of extraction well shows a drawdown of 0.3m. What is the coefficient of permeability of this aquifer? ( 4 marks)