You want to develop 3 sigma level process control charts to monitor the weight of boxes that contain trash. Due to different content of trash, weights are varying. You performed 4 samplings. Each time, they measured 3 boxes (n = 3). Draw control charts (you will have to choose proper control chart) and make conclusion whether things are under control.

Sampling 1	Sampling 2	Sampling 3	Sampling 4
20	28	24	28
24	30	28	20
26	24	26	26