Continuation of Exercise 4-138. Assume that the standard deviation of the size of a dot is 0.0004

Question:

Continuation of Exercise 4-138. Assume that the standard deviation of the size of a dot is 0.0004 inch. If the probability that a dot meets specifications is to be 0.9973, what specifications are needed? Assume that the specifications are to be chosen symmetrically around the mean of 0.002.