Option Explicit
Dim x As Single, y As Single, z As Single

Private Sub cmdD_Click()
    x = Val(txtX)
    y = Val(txtY)
    z = Val(txtZ)
    If x + y > z And y + z > x And z + x > y Then
        label.Caption = "YES"
    Else
        label.Caption = "NO"
    End If
End Sub