[lmikle]

Ну и ТЗ. В смысле, изложение...

Код:

procedure TForm1.Button1Click(Sender : TObject);
var
  S : Integer;
begin
  S := 0;
  If CheckBox1.Checked Then S := S + 8;
  If CheckBox2.Checked Then S := S + 15;
  If CheckBox3.Checked Then S := S + 20;

  If S = 0
    Then Label1.Caption := '000'
    Else Label1.Caption := IntToStr(S);
end;