ROC optimization
 

N12 M9 X6 ,GHD Purple Gift Set
average transaction price : = AMOUNT/V/100;
ROC: ( closing cost -REF ( mean transaction price ,GHD Midnight Gift Set 2011, N)) / REF ( mean transaction price ,GHD Purple Straighteners, N) * 100;
ROCMA: MA (ROC,GHD MK4 Kiss Straighteners, M);
ROCEMA: (2 * ROC + (X-1) * REF (ROC,GHD Blue Straighteners, 1)) / (X +1);