The manager of a loading dock is concerned about the time spent by her crew in nonproductive activities (e.g., waiting for paperwork, idle time, and the like.). Although she is not sure what the true proportion of nonproductive time is, she believes that it is close to 20 percent. If the manager wants to use work sampling to estimate this proportion with 95 percent confidence, a maximum error of 3.5 percent, how many samples should he or she take?