Question 608974
 l = 20 m, b = 15 m, and h = 6 m
 Capacity of the tank = lbh = (20 × 15 × 6) m3
 = 1800 m3
Water requirement per person per day = 150 litres
4000 * 150/1000 = 600 m ^3
1800/600 = 30 days