A monolithic floor system consists of 100 mm thick one-way slabs supported by beams 250 mm wide, 2.9 m on centers. The floor carries a superimposed dead load of 2.2 kPa and live load of 4.3 kPa. For a typical interior span of a slab, calculate the required spacing of top flexure bars. Use f'c = 21 MPa and flexure bar diameter 10 mm, grade 230 MPa. Express your answer in mm rounded down to a whole number.