大学的VB课程，不确定是什么问题

Question

{＆＃34;从字符串＆＃34转换;＆＃34;高级（65 +）＆＃34;＆＃34;输入＆＃39; Double＆＃39;无效。＆＃34;}

计划应该根据年龄和体育俱乐部的额外津贴来确定每月的费用

    Const Adult = 100D,
          Senior = 75D,
          Extras = 25D

    Const VBChecked As Decimal = 1
    Const VBUnchecked As Decimal = 0

    Dim Cost(3) As Decimal
    Cost(1) = 0D
    Cost(2) = 0D
    Cost(3) = 0D

    If (lst_Age.Items(1) = VBChecked) Then Cost(1) += Adult
    If (lst_Age.Items(2) = VBChecked) Then Cost(1) += Senior

    If (lst_Extras.Items(1) = VBChecked) Then Cost(2) += Extras
    If (lst_Extras.Items(2) = VBChecked) Then Cost(2) += Extras
    If (lst_Extras.Items(3) = VBChecked) Then Cost(2) += Extras

    Cost(3) = Cost(2) + Cost(1)
    Dim Output As Decimal = Cost(3)
    lbl_Output.Text = CDec(Output)