A Six Sigma level is calculated by which of the following equations:

A$.($Opportunities $+$ Defects$)/$Opportunities $x100$

B$.($Defects $-$ Opportunities$)/$Defects $x100$

C$.($Defects $+$ Opportunities$)/$Defects $100$

D$.($Opportunities $-$ Defects$)/$Opportunities x $100$