The inspection department in a cell phone final assembly plant checks cell phones coming off the line against 25 features that are considered critical-to-quality for customer satisfaction. During a one-month period, a total of 15,666 cell phones were produced. For those cell phones, a total of 1,055 defects of various types were found, and the total number of cell phones that had one or more defects was 320. Determine (a) the number of defects per million opportunities and corresponding sigma level, (b) the number of defects per million and corresponding sigma level, and (c) the number of defective units per million and corresponding sigma level.