How to convert answer into two decimal point

For formatting options, see this

Dim v1 as Double = Val(txtD.Text) / Val(txtC.Text) *
                   Val(txtF.Text) / Val(txtE.Text)
txtA.text = v1.ToString("N2");

Try using the Format function:

Private Sub btncalc_Click(ByVal sender As System.Object,
                          ByVal e As System.EventArgs) Handles btncalc.Click
  txtA.Text = Format(Val(txtD.Text) / Val(txtC.Text) * 
                     Val(txtF.Text) / Val(txtE.Text), "0.00")
  txtB.Text = Format(Val(txtA.Text) * 1000 / Val(txtG.Text), "0.00")
End Sub

If you have a Decimal or similar numeric type, you can use:

Math.Round(myNumber, 2)

EDIT: So, in your case, it would be:

Public Class Form1
  Private Sub btncalc_Click(ByVal sender As System.Object,
                            ByVal e As System.EventArgs) Handles btncalc.Click
    txtA.Text = Math.Round((Val(txtD.Text) / Val(txtC.Text) * Val(txtF.Text) / Val(txtE.Text)), 2)
    txtB.Text = Math.Round((Val(txtA.Text) * 1000 / Val(txtG.Text)), 2)
  End Sub
End Class