In a fed-batch culture, 200 g . L^–1 glucose solution is added at a flow rate of 50 L . h^–1. The initial culture volume (at quasi steady state) and the initial cell concentration are 600 L and 20 g . L^–1, respectively. The yield coefficient (Y_x/s) is 0.5 g cell mass . g substrate^–1. The cell concentration (g . L^–1) at quasi steady state at t = 8 h is ​