Control Charts of Xbar and R are maintained on dissolved iron content of a certain solution in ppm. After 2.5 hourly samples have been drawn and analysed, the data is organized into 25 subgroups of 5 measurements each, maintaining the time order of sampling.

From these data, sum of Xbar = 390.8 and sum of R = 84

Find the values of 3 sigma control limits of Xbar and R charts, and estimate the value of Standard Deviation for this process under the assumption that the process is in control.