Sample size of n = 7 items are taken from a manufacturing process. A quality characteristic is measured, and x and R values are calculated for each sample. The quality characteristic is normally distributed. After 30 samples, we have 30 30 Ex =2700 and ER. = 120 i-1 a) Compute central lines and 3-sigma trial control limits for the x and R charts. (11 points) b) Assume both charts exhibit in control, estimated process mean and standard deviation. (11 points)