Hello,everybody! I'll be glad if you help me!

Using the following data

30, 40, 50, 20, 20, 40.

construct 95% confidence interval estimate of the popolation mean.

What is the best formula for solving this problem?

E=t * S/sqrN(1)

or 1/2

E=Z * O/sqrN(2)

1/2

WHY?

Thanks for your time.