A prestressed concrete simply supported beam of span 6 m has a rectangular cross section 300 mm x 600 mm and unit weight of 24 KN/m3. The resultant prestressing tendon has zero eccentricity at ends and an eccentricity 'e' at midspan having linear profile. Under initial condition, the allowable stresses of the top and bottom of the section at midspan are +2 MPa (tension) and -20 MPa (compression) respectively. Using this condition, what is the prestressing force at midspan? Express your answer in KN and use one decimal place.