The dynamic method is used to measure ka in a fermenter operated at 30 C. Data for dissolved-oxygen concentration as a function of time during the re-oxygenation step us shown below. Time (s) CAL (% air saturation) 38.5 10 15 48.6 20 55.0 62.5 65.5 30 40 50 67.0 70 68.0 100 68.5 130 68.5 The equilibrium concentration of oxygen in the broth is 7.9 x 10-3 kg m3. Determine ka.