You should not be struggling with this. Go ahead and construct the confidence interval.

Find the Sample Mean.

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Find the Sample Standard Deviation.

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Find the Standard Deviation of the Sample Mean. <== This is the important part that will allow you to answer the second question.

? Mr F says: This is equal to where is the population standard deviation. If is unknown, it needs to be estimated by . If is large ( , although some books will say ) then and you can use the z-test. Otherwise you must use the t-test (assuming a roughly normal distribution).
Decide if you can use a z-score or a t-score.

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Find the right value for a 90% confidence interval. Is it one-tail or two-tail?

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That's a good start. Show us what you get and we can move on from there.