A water pumping system is driven by a horizontal axis multi-bladed wind turbine at a power coefficient (C_p) of 0.4. The total pumping head and discharge are 20 m and 15 L s⁻¹, respectively. The mean wind velocity is 8 m s⁻¹ and the pump efficiency is 70%. The density of air and water are 1.2 and 1000 kg m⁻³, respectively. If the transmission efficiency from wind turbine to the pump is 90%, the required diameter of the wind turbine in m (round off to 2 decimal places) is _______.