static public void CalculatePersonTotalMoney(List <Person> personList, List <Thing> thingList) { foreach (var item in personList) { item.TotalMoney = DataProcessing.CalculateMoney(item.Pen, thingList.Sum(x => x.Pen)) + DataProcessing.CalculateMoney(item.Pen, thingList.Sum(x => x.Pencil)) + DataProcessing.CalculateMoney(item.Eraser, thingList.Sum(x => x.Eraser)) + DataProcessing.CalculateMoney(item.Ruler, thingList.Sum(x => x.Ruler)) + DataProcessing.CalculateMoney(item.LiWhite, thingList.Sum(x => x.LiWhite)); } }