Вывод результата переменных в конце программы

Function WritePeremen()
Dim a3, a4, y1, y2, x1, x2, a, b, c, D As Integer
a3 = InputBox("Write a3", "Write")
a4 = InputBox("Write a4", "Write")
a = 3
b = (-3 * a3) / (2 * a4)
c = (-1) / (2 * a4) + 9
D = b ^ 2 - 4 * a * c
x1 = ((-b) - Sqr(D)) / (2 * a)
x2 = ((-b) + Sqr(D)) / (2 * a)
y1 = (-2) * x1 ^ 2 + 8
y2 = (-2) * x1 ^ 2 + 8
MsgBox = x1
MsgBox = x2
MsgBox = y1
MsgBox = y2
End Function

Sub WritePeremen()
    Dim a3 As Double, a4 As Double, y1 As Double, y2 As Double
    Dim x1 As Double, x2 As Double, a As Double, b As Double, c As Double, D As Double
    a3 = Val(Replace(InputBox("Write a3", "Write", 10.6), ",", "."))
    a4 = Val(Replace(InputBox("Write a4", "Write", 1.3), ",", "."))
    a = 3
    b = (-3 * a3) / (2 * a4)
    c = (-1) / (2 * a4) + 9
    D = b ^ 2 - 4 * a * c
    If D < 0 Then MsgBox "D < 0. Решений нет!": Exit Sub
    x1 = ((-b) - Sqr(D)) / (2 * a)
    x2 = ((-b) + Sqr(D)) / (2 * a)
    y1 = (-2) * x1 ^ 2 + 8 'Что-то не так - две одинаковые строки.
    y2 = (-2) * x1 ^ 2 + 8 'Что-то не так - две одинаковые строки. Наверное здесь должно быть y2 = (-2) * x2 ^ 2 + 8
    MsgBox "x1 = " & x1 & vbCrLf & _
           IIf(D = 0, "", "x2 = " & x2 & vbCrLf) & _
           "y1 = " & y1 & vbCrLf & _
           "y2 = " & y2
End Sub