Answer: t=-5.651
Step-by-step explanation:
Let
be the population mean number of hours a week answering their email.
As per given we have

Sample size : n= 783
Sample mean :

Sample standard deviation: s=7.23
Since population standard deviation is unknown, so our test -statistic has a t-distribution.
Test statistic :


∴ The test statistic : t=-5.651