This is the famous Napkin model in QM exam. Professor didn't want to return my own work this is just the best of my guess work. I know exactly what I have done wrong, i.e. the dotted line between D1 to D2 to D3 to D4. To aide memoir D1=day 1, EOS=express overnight service, SS=standard service, NEW=new purchase, SOLD=napkin sold.