You plated diluted saliva samples on Petrifilms and counted…

You plated diluted saliva samples on Petrifilms and counted the following numbers of colonies for each dilution:  Dilution Factor 10-4 10-5 10-6 10-7 10-8 CFU/mL 1089 756 432 244 15 Which dilution factor should you use to calculate the initial CFU/mL of your sample?