a MD public health official is alarmed at the sodium levels in big-chain store burritos. The official goes to a nearby big-chain store and takes a...

a MD public health official is alarmed at the sodium levels in big-chain store burritos. The official goes to a nearby big-chain store and takes a sample of n=15 burritos orders. she finds that the mean sodium level is 2000mg and standard deviation is 200mg. Find the 95% confidence interval for the mean sodium level.

This is my calculation:2000+-1.96*200/sqrt of 15

2000+-1.96 = 1998.04 - 2001.96

2000(95% c.i. 1998 - 2001.96)

Margin of Error = 101.21

I got this wrong as it was looking for the t-distribution method.