A rectangular concrete beam of width 120 mm and depth 200 mm is prestressed by pretensioning to a force of 150 kN at an eccentricity of 20 mm. The cross-sectional area of the prestressing steel is 187.5 mm². Take modulus of elasticity of steel and concrete as 2.1 _^x10⁵ MPa and 3.0 _^x10⁴ MPa respectively. The percentage loss of stress in the prestressing steel due to elastic deformation of concrete is