主题：求助一个难题

逻辑如下，请自行琢磨：

Dim st As Date = #1/5/2012# ' 开始日期
Dim et As Date = #2/25/2012# '结束日期
Dim qd As String = "丰田金融" '融资渠道
Dim je As Double = "300000" '贷款金额
Dim lx As Double
Dim ld As Date = st
Dim drs As List(of DataRow) = DataTables("利率维护").Select("融资渠道 = '" & qd & "'")
For Each dr As DataRow In drs
    If dr("利率调整开始日期") > ld Then
        If dr.IsNull("利率调整终止日期") OrElse dr("利率调整终止日期") > et Then
            lx = lx + dr("现行利率") * (st - ld).TotalDays  '自己调整计算方式
            Exit  For
        ElseIf dr("利率调整开始日期") > ld Then
            Dim nld As Date
            Dim ned As Date
            If dr("利率调整开始日期") > ld Then
                nld = dr("利率调整开始日期")
            Else
               nld = ld 
            End If
            If dr("利率调整终止日期") > et Then
                 ned = et
            Else
                ned = dr("利率调整终止日期")
            End If
            lx = lx + (ned - nld).TotalDays * dr("现行利率")
            ld = ned
        End If
    End If
Next