Confidence Interval, unknown stand dev

...nvrm solved it myself....

Assuming that the population is normally distributed, construct a 95% confidence interval for the population mean, based on the following sample size n = 7: 1, 2, 3, 4, 5, 6, and 20. Change the number 20 to 7 and recalculate the confidence interval. Using these results, describe the effect of an outlier on the confidence interval.

My attempt:

My answer for the first part of this question is wrong, I don't think I know how to properly take the standard deviation. Please check and correct.

Answer for first part: