An existing bubble$-$cap distillation tower has an ID of $8ft$ and a tray spacing of $30in.$ The tower is operating under a pressure of $70$ psig, and a slot liquid seal of $2in.$ is maintained. At the point of maximum volumetric vapor flow, the molecular weight of the vapor is $100,$ the $55l\frac{b}{f}{t}^3$ and $1\mathrm{.}24l\frac{b}{f}{t}^3$ respectively. And the temperature is $175F,$ The pressure drop through the tower is negligible, and the ideal gas law is applicable to the rising vapors. Approximately what percent of the maximum allowable flow rate is being used in the tower?