A manufacturing facility uses a four-step process to assemble an automotive component. The quality auditors have noticed that the quality of the first step is at the 4.5 sigma level, and the quality of the second step is at the 5 sigma level. both the third and fourth steps are at the 5.5 sigma level, what is the sigma level of the entire process? How is the percentage of error outcome or yeild calcualted when the only data given is the sigma level for each step?