A retailer wants to evaluate the effectiveness of a new marketing campaign on increasing sales. The retailer randomly selects 100 customers who received a promotional email and 100 customers who did not receive the email. The retailer compares the average purchase amount for each group to determine if there is a significant difference in the mean purchase amount between the two groups. The sample mean purchase amount for customers who received the email is $150 with a standard deviation of $20, while the sample mean purchase amount for customers who did not receive the email is $140 with a standard deviation of $25. Conduct a hypothesis test with a 5% significance level to determine if the new marketing campaign has a significant effect on the mean purchase amount.