A first-order homogeneous liquid-phase reaction ($A \rightarrow B$) occurs in a non-ideal isothermal reactor operating at steady state. The variance ($\sigma^2$) of residence time distribution (RTD) from a pulse tracer experiment is $4 \text{ min}^2$. The volumetric flow rate of the feed is $5 \text{ L min}^{-1}$ and volume of the reactor is $25 \text{ L}$. The reaction rate constant is $0.4 \text{ min}^{-1}$. Based on the tanks-in-series model, the conversion (in \%) is _______ (rounded off to one decimal place).