Many college graduates who are employed full-time have longer than -hour work weeks. Suppose that we wish to estimate the mean number of hours, , worked per week by college graduates employed full-time. We'll choose a random sample of college graduates employed full-time and use the mean of this sample to estimate . Assuming that the standard deviation of the number of hours worked by college graduates is hours per week, what is the minimum sample size needed in order for us to be confident that our estimate is within hours per week of