The 3-sigtna limits for X and R control charts, with the sample size of n=4 are given as follows: UCL=815 UCL=46.98 CL=800 CL=20.59 LCL=785 LCL=0 Assume the process is in control and LSL = 790, USL=810. a) What is the estimated process standard deviation? (6 points) b) Calculate the PCR for the process. Is the process capable? (6 points) c) What is the percentage of nonconforming parts? (6 points) d) Comment on how the process nonconforming units can be reduced. (3 points)