An e-marketing consultant is hired to determine how long customers spend, on average, on a company's website. If the standard deviation is known from previous studies to be approximately 6 minutes, determine the number of customers that needs to be sampled in order to determine the mean length of time spent on the company's website, accurate to within a margin of error of 0.7 minutes, at the 20% level of significance. Standard Normal Distribution Table Number of Customers = Round up to the next whole number