private void mnThanhToan_Click(object sender, System.EventArgs e)
        {
            frmTraPhong f = new frmTraPhong();

            f.MdiParent = this;
            f.Show();
        }
 private void mnThanhToan_Click(object sender, System.EventArgs e)
 {
     frmTraPhong f = new frmTraPhong();
     f.MdiParent=this;
     f.Show();
 }