Suppose a random sample of size 31 produced a mean of 87.44 with a standard deviation of 13.858 . Determine a $90 \%$ confidence interval for the population mean. Enter only the RIGHT (upper) endpoint of the interval below. Round your answer to 2 decimal places.

Step 1 ：We are given a random sample of size 31 which produced a mean of 87.44 and a standard deviation of 13.858. We are asked to determine a 90% confidence interval for the population mean.

Step 2 ：The formula for the confidence interval for a population mean is \(\bar{x} \pm Z \frac{s}{\sqrt{n}}\), where \(\bar{x}\) is the sample mean, \(Z\) is the Z-score, \(s\) is the sample standard deviation, and \(n\) is the sample size.

Step 3 ：In this case, we are asked to find the right endpoint of the 90% confidence interval, so we only need to add the margin of error to the sample mean.

Step 4 ：The Z-score for a 90% confidence interval is approximately 1.645.

Step 5 ：Substituting the given values into the formula, we get the margin of error as 4.0943561031761915.

Step 6 ：Adding the margin of error to the sample mean, we get the right endpoint of the confidence interval as 91.53.

Step 7 ：Final Answer: The right (upper) endpoint of the 90% confidence interval for the population mean is \(\boxed{91.53}\).