Thirty-five samples of size 7 each were taken from a fertilizer-bag-filling machine. The results were: overall mean

Question:

Thirty-five samples of size 7 each were taken from a fertilizer-bag-filling machine. The results were: overall mean = 57.75 lb; Average range = 1.78 lb.
(a) Determine the upper and lower control limits of the x-chart, where σ = 3.
(b) Determine the upper and lower control limits of the R-chart, where σ = 3.