The document describes an artificial transformation experiment using an XL1-Blue II bacterial culture with an optical density (OD) of 0.68. To calculate the total number of cells: the OD of 1 equals 1x108 cells/ml, so an OD of 0.68 equals 6.8x108 cells/ml. The document asks how many total cells were in the cell pellet after spinning down 1.5ml of this culture in an Eppendorf tube.