To protect a wheat field from wind erosion, windbreaks of 2.7 m height are provided. The actual wind velocity at 15 m height perpendicular to the wind barrier is 9 m.s^-1 and the minimum wind velocity at 15 m height required to move the most erodible soil fraction is 9.6 m.s^-1. The distance of full protection from this windbreak is ______ m. (Rounded off to 2 decimal places)