Researchers were curious about the size of the bills at restaurants based on whether a credit card was used to pay versus cash. The researchers took random samples of bills at restaurants across the US, and these sample statistics are summarized in the table below a. Is there evidence of a difference in the mean size of the restaurant bill depending on the method of payment? Do the appropriate statistical analysis (confidence interval or hypotheses test) and show all steps involved in answering this question. b. Can the results of this study be generalized to all restaurants across the US? Why or why not, based on the methodology and results of the study?