Correct format for mathematical calculations

Would this be a proper math equation for making sure that the Textboxes are being read as numbers? Please Change if not a good way! Thanks for any suggestions!!!
Dim a1, a2, a3, a4, a5, a6, x As Integer
a1 = Val(Text20.Text)
a2 = Val(Text33.Text)
a3 = Val(Text32.Text)
a4 = Val(Text45.Text)
a5 = Val(Text57.Text)
a6 = Val(Text69.Text)
x = a1 - a2
Text45.Text = x
x = a3 * a4
Text57.Text = x
x = a5 - a6
Text81.Text = x