49. A major retail clothing store is interested in estimating the difference in mean monthly purchases by customers who use the store's in-house credit card versus using a Visa, Mastercard, or one of the other major credit cards. To do this, they have randomly selected a sample of customers who have made one or more purchases with each of the types of credit cards. The following represents the results of the sampling: In-House Credit Card National Credit Card Sample Size: 86 113 Mean Monthly Purchases: $45.67 $39.87 Standard Deviation: $10.90 $12.47 Based on these sample data, what is the lower limit for the 95 percent confidence interval estimate for the difference between population means? a. About $5.28 b. Approximately $4.85 c. Approximately $2.54 d. Approximately $3.41