30 patients diagnosed with insomnia subscribed to the Calm app. After a follow-up of one month, the mean of the differen

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30 patients diagnosed with insomnia subscribed to the Calm app.
After a follow-up of one month, the mean of the differences between
the current and the past sleep durations turned out to be 1.46
hours with a sample standard deviation of 2.5 hours. We wish to
test whether using the Calm app leads to increased sleep duration
in patients diagnosed with insomnia at 0.05 level of significance.
The data in this question leads to
a.) a t-statistic equal to 3.199 with df=30.
b.) a z-statistic equal to 3.199
c.)a t-statistic equal to 3.199 with df=29.
d.)a t-statistic equal to 0.584 with df=29.
e.) a t-statistic equal to 17.52 with df=29.