Analysis showed that the mean arrival rate for vehicles at a certain Shell station on Friday afternoon last year was 4.5 vehicles per minute. How large a sample would be needed to estimate this year's mean arrival rate with 98 percent confidence and an error of ± 0.5? (Round the standard deviation answer to 4 decimal places. Enter your answer as a whole number (no decimals). Use a z-value taken to four decimal places in your calculations.) Sample size