A post-tensioned concrete beam, 100 mm wide and 300 mm deep,.. is prestressed by three cables, each with a cross-sectional area of 50 mm and with an initial stress of 1200 N/mm. All the three cables are straight and located 100 mm from the soffit of the beam. If the modular ratio is 6, calculate the loss of stress in the three cables due to elastic deformation of concrete for only the following cases: (a) simultaneous tensioning and anchoring of all the three cables; and (b) successive tensioning of the three cables, one at a time.