The manager of a mall conducted a survey among two groups (n1 = 100, n2 = 100) of visitors to the mall on different days. She found that the first group spent an average of 60 minutes in the mall, while the second group spent an average of 90 minutes in the mall. If the manager wishes to see the difference in the average times spent by the two groups in the mail, which of the following sets shows the null hypothesis and alternative hypothesis