What is the standard error for the following scenario?

Helen is reporting the average production length for a certain part of a machine from a sample of 100 items. The average of the sample is 78 cm with the sample's standard deviation of 0.66 cm. She is reporting the average with 90% confidence.

Select one:a. 51.48

b. 0.11

c. 0.66

d. 0.066