Действия над элементами массива - VB

Private Sub Command1_Click()
Dim a, b, c
Dim mv1, mv2, mv3 As Double
a = Array(17.2, 9.3, 14.5, -11.7, 4.3, 5.9, -11.9, 12.3, -14.1, -15.3)
b = Array(-1.2, 4.2, 5.9, 18.1, 21.2, 3.1, -5.3, -12.7, 21.4, -4.5, 8.2, 9.4)
c = Array(3.5, 8.4, -3.2, 4.5, 8.4, 9.5, 15.4, 9.3)

mv1 = MiddleValue(a)
mv2 = MiddleValue(b)
mv3 = MiddleValue(c)
 
MsgBox "среднее арифметическое : " & vbCrLf _
        & "ГЂ = " & Format(mv1) & vbCrLf _
        & "B = " & Format(mv2) & vbCrLf _
        & "C = " & Format(mv3)
 
End Sub
 
Function MiddleValue(ByVal S As Long) As Long
    Dim n, i, st, k As Double
    n = Val(InputBox("введите кол-во элементов массива : "))
    st = 0
    k = 0
    For i = 1 To n
             If S(i) > 0 Then st = st + S(i) And k = k + 1
    Next i
    MiddleValue = st / k
End Function