In a fed-batch culture, $200 \text{ g . L}^{-1}$ glucose solution is added at a flow rate of $50 \text{ L . h}^{-1}$ . The initial culture volume (at quasi steady state) and the initial cell concentration are $600 \: L$ and $20 \text{g . L}^{-1}$ , 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
- $40$
- $52$
- $60$
- $68$