For patients who have been given a diabetes test, blood-glucose readings are approximately normally distributed with mean 129 mg/dl and a standard deviation 10 mg/dl. Suppose that a sample of 3 patients will be selected and the sample mean blood-glucose level will be computed.

Enter answers rounded to three decimal places.

According to the empirical rule, in 95 percent of samples the SAMPLE MEAN blood-glucose level will be between

the lower-bound of?? and the upper-bound of??

How do I solve this? I've tried doing standard deviation of + and - 2 and it hasn't worked