A prestressed concrete beam 150 mm x 300 mm supports a live load 5 KN/m over a simply supported span of 8 m.It has a parabolic cable having an eccentricity of 75 mm at mid span and zero at the ends. The prestressing force required to maintain the net resultant stress at the bottom fibre at mid span as zero under the action of D.L (Dead Load) + L.L (Live load) + prestress is -