VB Program for college, Unsure what is wrong
<p>{"Conversion from string "" Senior (65+)"" to type 'Double' is not valid."}</p>

<p>Program is supposed to determine cost per month based on age, and extra perks for a sports club</p>

<p><a href="https://i.stack.imgur.com/ZOr8L.png" rel="nofollow"><img src="https://i.stack.imgur.com/ZOr8L.png" alt="layout"></a></p>

<pre><code>    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)
</code></pre>