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, it has 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 Suppose that the managers wished to test whether there is a statistical difference in the mean monthly purchases by customers using the two types of credit cards, using a significance level of 0.05, what is the value of the test statistic assuming the standard deviations are known? Round to two decimal places.