Can you go into detail for this question because I have trouble with the last step for b and c.

3. The diameter of PingPong balls manufactured at a large company is normally distributed with a population mean of u = 1.3 inches and a standard deviation of o = .04 inches. The quality control department selects several random samples of N =36 Ping-Pong balls. 3. What is the expected value of the mean? What is the standard error of the mean ( keep 4 decimals for your answer and for calculations b-d)? b. What percentage of the sample means will be less than 1.287 inches? 0. What percentage of the sample means will be between 1.2868 and 1.3132 inches? d. What two sample means form the boundaries for the middle 60% of the distribution? ( Hint: You will need to convert the z-values into sample means.)