NEED Help how would you solve for part a and part b?

a

Based on samples of 15 IRS tax auditors, each handling 250 files, we find that the total number of mistakes in handling files is 415.a)Find the 99.73% upper and lower control limits.b)Three more auditors were then reviewed, and the number of errors in each of their 250 files were:25, 28 and 49.Is this tax auditing process in control?

b

There have been complaints by subscribers that there were many errors on the pages of the Joliet Tribune. The last 6 days have been examined carefully and the number of errors are recorded below. Is the process in control usingZ= 3?