This is how I set up the data in Excel, showing the given mean and standard deviation of the sample, and the required confidence level for the interval. Alpha, the significance level, is 100-(Confidence Level), and we ask Excel to find the critical value using the CONFIDENCE.T function, which has three parameters: alpha, standard deviation and sample size=6. The result is Disp (for displacement).
Low and High show the lower and upper limits.
Excel will use a 2-tail t-distribution with 5 degrees of freedom (sample size-1=5) to determine the multiple of s that will be used to calculate the interval. Excel divides s by √6 to derive the margin of error. The Confidence Interval, CI=x̅±Disp=85±8.40 (2 dec place accuracy), giving Low and High extremes of the interval.