Many physical processes are exponential in nature. A typical way of cleaning a tank of contaminated water is to run in clean water at a constant rate, stir, and let the mixture run out at the same rate. Suppose there are initially 100 pounds of a contaminant in a large tank of water. Assume that the cleaning method described above removes 40% of the remaining contaminant each hour. Round your answer to one decimal place. How much contaminant is removed from the tenth (t = 10) to the thirteenth (t = 13) hour of the cleaning process?