Which formula does Google use to rank keyword-targeted ads on Google Search

Which formula does Google use to rank keyword-targeted ads on Google Search
  A)  (Maximum cost-per-click (CPC) bid + Daily Budget) / Quality Score
  B)  Maximum cost-per-click (CPC) bid x Quality Score
  C)  (Maximum cost-per-click (CPC) bid x Quality Score) / Daily Budget
  D)  Maximum cost-per-click (CPC) bid only