The Arbograss report confirmed that water usage of guest showers was also normally distributed with a mean of 30 gallons and a standard deviation of 10 gallons. d) (5 pts) Suppose that Bates wants to collect his own data on water usage. He wants to compute a 95% confidence interval of the form + 1 gallon for the true mean water usage of a shower. Assuming Arborgrass' estimate of standard deviation is accurate, how many showers must Bates monitor in total to be able to compute such a confidence interval