What is the Confidence interval of this...?

#1
HI Friends,

I've attached excel sheet having 19 records. Can you guys pls help me in finding 95% confidence interval for this. I tried finding it all way, but I'm not getting correct answer.

Should t- distribution or Normal distribution be used..?

I Thank in advance. Pls help me in finding right answer friends.

Mahesh
 

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