如何在动态对象中使用linq Sum

在数据访问层我有以下查询:

var result = from income in context.Incomes
                join order in context.Orders on income.OrderId equals order.OrderId
                select new
                {
                    Voucher = order.VoucherSeries + "-" + order.VoucherNumber,
                    Amount = income.IncomeAmount
                };
return result.ToList();

在业务层如何使用linq Sum作为Sum Amount?