A researcher is trying to determine the doubling time for a population of the bacterium Giardia lamblia. He starts a culture in a nutrient solution and estimates the bacteria count every four hours. His data are shown in the table. Time hours 0 4 8 12 16 20 24 Bacteria count CFU/mL 37 47 63 78 105 130 173 a Make a scatter plot of the data. b Use a graphing calculator to find an exponential curve f(t)=abt that models the bacteria population t hours later. c Graph the model from part b together with the scatter plot in part a Use the TRACE feature to determine how long it takes for the bacteria count to double.