We want to study the difference in means when a group of people pays individually for a dinner versus splitting the bill equally (as a group). We have a group of 40 people who split the bill equally - their sample mean cost was $50.92 with a sample standard deviation $14.33. We also have another group of 40 people who paid for dinners individually - their sample mean cost was $38.78 with a sample standard deviation of $12.54. Find a 95% confidence interval forS I , the difference in population means costs between people who split their bills equally and people who pay their bills individually.