4. Shafts manufactured for use in optical storage devices have diameters that are normally distributed with mean u = 0.656 cm and standard deviation 6 = 0.004 com. The specification for the shaft diameter is 0.652 + 0.006 cm. a) What proportion of the shafts manufactured by this process meet the specifications? (4 points) b) The process mean can be adjusted through calibration. If the mean is set to 0.651 cm, what proportion of the shafts will meet specifications? (4 points) c) If the mean is set to 0.651 cm, what must the standard deviation be so that 92% of the shafts will meet specifications? (4 points)