A producer of cell phones checks each phone prior to packaging, using seven critical-to-quality (CTQ) characteristics that

Question:

A producer of cell phones checks each phone prior to packaging, using seven critical-to-quality (CTQ) characteristics that are deemed important to customers. Last year, out of 205,438 phones produced by the company, a total of 578 phones had at least one defect, and the total number of defects among these 578 phones was 1692. 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.