A survey is being planned to determine the mean amount of time corporation executives watch television. A pilot survey indicated that the mean time per week is 18 hours, with a standard deviation of 5.0 hours. It is desired to estimate the mean viewing time within one-quarter hour. The 95% level of confidence is to be used.
How many executives should be surveyed? (Round your z-score to 2 decimal places and round your final answer to the next whole number.)