Please help on this Quality Control question

Question $4[10$ marks$]$

The performance of the first shift is reflected in the inspection results of electric carving knives.

a$)$ Determine the trial central line and control limits for each subgroup. $[6$ marks$]$

b$)$ Assume that any out$-$of$-$control points have assignable causes and determine the standard value

for fraction nonconforming for the next production period. $[4$ marks$]$