Selecting text in vb - vb.net

Question

I want to select a word to another word in a text box in vb.net with everything between them highlighted.
an example is
I went to the beach, had a pinic with my family and then went home at 6 o clock.
The starting word to be had and the end word being home and everything highlighted in between.
I have already used a little bit of code
Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
Dim a As String
Dim b As String
a = TextBox2.Text 'means what ever is in textbox2 string to the location where "a" is
b = InStr(RichTextBox1.Text, a)
If b Then
RichTextBox1.Focus()
RichTextBox1.SelectionStart = b - 1
RichTextBox1.SelectionLength = Len(a)
but its not exactly what i want it to do.
Addition to this was using RegEx Function as shown below
'gets rid of the enter line break eg <enter> command no new lines
Dim content As String = Replace(TextBox1.Text, Global.Microsoft.VisualBasic.ChrW(10), Nothing)
'searches for this tag in the brackets between ".*" will be the contents
Dim Regex As New Regex("<div.*class=""answer_text"".*id=editorText"".*""")
'Show the string
For Each M As Match In Regex.Matches(content)
'This will get the values, there are 3 atm meta.name des and content
Dim Description As String = M.Value.Split("""").GetValue(3)
'displays the content in the label
TextBox3.Text = "" & Description
Next

Answer 1

This will select everything between startWord and endWord excluding them both
Dim startWord As String = "had"
Dim endWord As String = "home"
Dim index As Integer = richTextBox1.Text.IndexOf(startWord)
richTextBox1.[Select](index + startWord.Length, richTextBox1.Text.IndexOf(endWord) - index - startWord.Length)

Answer 2

Here's a solution involving two TextBox controls:
Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
Dim a As String
Dim b As String
Dim index_a As Integer
Dim index_b As Integer
a = TextBox1.Text
b = TextBox2.Text
index_a = InStr(RichTextBox1.Text, a)
index_b = InStr(RichTextBox1.Text, b)
If index_a And index_b Then
RichTextBox1.Focus()
RichTextBox1.SelectionStart = index_a - 1
RichTextBox1.SelectionLength = (index_b - index_a) + Len(b)
End If
End Sub
TextBox1 contains the first word, TextBox2 contains the second word. When clicking the button, it will highlight from the first word to the end of the second word.