Select the correct answer from each drop-down menu. Gary is testing a river water sample in his lab. Initially, there are 64 bacteria in the river water sample. The number of bacteria after 3 hours can be calculated using the expression shown below. Use the given expression to complete the statements. The quantity that represents the initial number of bacteria is . The quantity that represents the rate at which the number of bacteria is increasing is , which means the growth rate percentage for the bacteria is %.