Question 1185014
The sample of 16 is normally distributed with the sample average 12 mm , same as the sample, and the sd 4/sqrt(16) or 1 mm.
The sample mean < 15.6 mm is a z=(x bar -mean)/sigma/sqrt(n)
This is  z < 3.6/1 or 0.9998
Between 12.8 mm and 13.2 mm is z between 0.8 and 1.2, or probability of 0.0968.