Adjust size of Child Forms

See more:

VB

I have Windows 7 with Visual Basic 2010.

In my application I have a parent form named: Form1
that hosts two Child forms: Child1Form1 and ChildForm2

I have written the following code:

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim DeskHeight As Integer : Dim DeskWidth As Integer
        DeskWidth = Screen.PrimaryScreen.WorkingArea.Width
        DeskHeight = Screen.PrimaryScreen.WorkingArea.Height
        Me.Show()
        Me.Size = New Size(DeskWidth, DeskHeight)
        Dim Location As Point : Location = New System.Drawing.Point(0, 0)
        Me.Location = Location
        Location = New System.Drawing.Point(0, 0)
        Me.Location = Location
        '--------------------------
        ChildForm2.MdiParent = Me
        Childform2.Location = New Point(175, 0)
        Childform2.Show()
        Dim ChildForm2Width, ChildForm2Height As Integer
        ChildForm2Width = DeskWidth - 175
        Childform2.Size = New Size(ChildForm2Width, DeskHeight)
        Location = New System.Drawing.Point(175, 0)
        Childform2.Location = Location
        ChildForm2.Text = "Child2"
        '-----------------------------
        ChildForm1.MdiParent = Me
        Childform1.Show()
        Childform1.Size = New Size(175, DeskHeight)
        Location = New System.Drawing.Point(0, 0)
        Childform1.Location = Location

    End Sub
End Class

My problem is how to make the two child forms fit inside Form1.
If Childform1 has a width of 175 as I set, then Childform2 width
should be:

Deskwidth-175

But this does'nt work. The working area for the child forms is smaller.
I have the same problem for the height of the child forms.
How can I calculate the working area (height -width) of the child forms so no scroll bars appeare ?