Replication and division of nuclei and cells — practice question

A bacterial culture was grown so that it replicated with nucleotides containing the heavy nitrogen isotope ($^{15}\text{N}$). After a number of generations, every bacterial DNA molecule contained heavy nitrogen. A DNA sample was removed from the culture, combined with caesium chloride solution and then centrifuged at high speed. During this procedure, DNA molecules with different masses separate into bands at different places in the centrifuge tube. The greater the mass of the DNA molecules, the nearer the bottom of the centrifuge tube the band appears. The diagram shows where the DNA molecules containing heavy nitrogen are located in the centrifuge tube. The bacterial culture was then grown using nucleotides containing the light nitrogen isotope ($^{14}\text{N}$). DNA samples were collected and separated by centrifugation after the bacteria had divided once and then again after they had divided twice. At which positions would the DNA be present after one cell division and after two cell divisions?