Answer:

Theoretically: yes, because we can estimate x(0) and K, so $y_{XS} = X(0)/(K \, x(0))$. This is remarkable, because we have no direct measurements about the conversion from substrate to biomass. Practically, however, we will see that in presence of a little scatter, the uncertainty in the values for x(0) and K is large, which makes the uncertainty in the value of y_XS huge.