20. Hard Hats The safety requirements for hard hats worn by construction workers and others specify that each of three hats pass the following test. A hat is mounted on an aluminum head form. A 3.5-kilogram steel ball is dropped on the hat from a height of 1.5 meters, and the resulting force is measured at the bottom of the head form. The force exerted on the head form by each of the three hats must be less than 4000 Newtons, and the average of the three must be less than 3400 Newtons. (The relationship between this test and actual human head damage is unknown.) Suppose the exerted force is normally distributed, and hence a sample mean of three force measurements is normally distributed. If a random sample of three hats is selected from a shipment with a mean equal to 3600 and s 5400, what is the probability that the sample mean will satisfy the safety requirement?