Make VB Program Look For Files In The Same Folder It Is Running From?

I need to have my VB program look for two specific programs in the same folder it is running from. How do I do that?Here is the code for when I run my program. I need it to look for the files that are underlined. They are the tpfh20 and tphd20.

Private Sub btnRunRelap5_Click(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles btnRunRelap5.Click

Dim pathString As String = String.Format("relap5 -i {0} -o {1} -r {2}", txtInput.Text, txtOutput.Text, txtRestart.Text)Dim stripString As String = String.Format(" -s {0}", tbStripFile.Text)
Dim guiString As String = " -n gui"
Dim waterprop As String = " -w tpfh20 -d tphd20"
If Not lblChangeStripFile.Visible Then

[Code]...