12.4-2. Height of Tower in Ion-Exchange. In a given run using a flow rate of 0.2 m³/h in an ion-exchange tower with a column height of 0.40 m, the break point occurred at 8.0 min. The ratio of usable capacity to total equilibrium capacity is 0.65. What is the height of a similar column operating for 13.0 min to the break point at the same flow rate?