Crops are grown in a field having soil, which has field capacity of 30% and permanent wilting point of 13%. The effective depth of root zone is 80 cm. Irrigation water is supplied when the average soil moisture drops to 20%. Consider density of the soil as 1500 kg/m³ and density of water as 1000 kg/m³. If the daily consumptive use of water for the crops is 2 mm, the frequency of irrigating the crops (in days), is