The rate of growth of a certain cell culture is proportional to its size. In 10 hours a population 1 million cells grew to 5 million?. How large will the cell culture be after 15 hours?.The population of the cell culture after 15 hours will be_ million

The rate of growth of a certain cell culture is proportional to its size. In 10 hours a population of 1 million cells grew to 5 million. How large will the cell culture be after 15 hours? The population of the cell culture after 15 hours will be million. (Round the final answer to the nearest million as needed. Round all intermediate values to the nearest thousandth as needed.)