A biologist wishes to estimate the effect t of an antibiotic on the growth of a particular bacterium by examining the mean amount of bacteria present per plate of culture when a fixed amount of the antibiotic is applied. Previous experimentation with the antibiotic indicates that the standard deviation of the amount of bacteria present is approximately 13cm2. Use this information to determine the number of observations (cultures that must be developed and then tested) to estimate the mean amount of bacteria present, using a 99% confidence interval with a half-width (margin for error) of 3cm2