I have a easy problem that i can't figure out, here is the code

Private Sub Command1_Click()

a = Text1.Text
b = Text2.Text
c = Text3.Text

d = a + b + c

Text4.Text = d

End Sub

The problem is if you enter a number into TEXT1,TEXT2,and TEXT3, the result is not added together.
Example: TEXT1 = 4
TEXT2 = 5
TEXT3 = 6

The resultis 456, but i need it to do the addition??
Any ideas??
Altecjjf