Type the correct answer in the box. Round your answer to the nearest hour. A scientist running an experiment starts with 100 bacteria cells. These bacteria double their population every 15 hours. Find how long it takes for the bacteria cells to increase to 300. Use the formula , where is the original number of bacteria cells, is the number after t hours, and d is the time taken to double the number. It takes 15 hours for the number of bacteria to increase to 300.