Problem $10-7($Algo$)$

The postmaster of a small western town receives a certain number of complaints each day about mail delivery.

Click here for the Excel Data File

a$.$ Determine two$-$sigma control limits using the above data. $($Round your intermediate calculations to $4$ decimal places

and final answers to $3$ decimal places. Leave no cells blank $-$ be certain to enter $"0"$ wherever required. Round up any negative

control limit value to zero.$)$

Please explain your answer, use excel sheet with formulas. I dont understand this question. Thank you :)