A Class 1 post-tensioned concrete beam is simply supported over a 10 m span. The characteristic imposed load consists of a concentrated force of 100 KN at the midspan. The characteristic concrete strength is 50 N/mm² and the unit weight of concrete is 25 kN/m³. The beam is of a uniform section having the dimensions 350 mm (width) x 600 mm (height). Concrete strength at transfer is 40 N/mm² and the prestress loss at transfer is 20%. Determine the maximum economic prestress and the corresponding tendon width at the mid-span.