VB.NET如何进行线性插值计算？

VB.NET如何进行线性插值计算？
比如说一组数据：X分别是0 5 10 15 20；相对应Y为0 0.1 0.4 0.7 0.8。计算X=7时，Y是多少？

        Dim divIn() As Double = {0, 5, 10, 15, 20}
        Dim divOut() As Double = {0, 0.1, 0.4, 0.7, 0.8}
        Dim x As Double = 7
        Dim y As Double = 0
        For i As Integer = 0 To divIn.Length - 2
            If x > divIn(i) And x <= divIn(i + 1) Then
                y = (divOut(i + 1) - divOut(i)) / (divIn(i + 1) - divIn(i)) * (x - divIn(i)) + divOut(i)
            End If
        Next
        MessageBox.Show(y)