//Precondition: must be letters in the parcels list
//Postcondition:displays all the letter info(origin/destination/fixed cost) for each letter
// object in the parcels list. And adds the total cost of all parcels in the list
private void listParcelToolStripMenuItem_Click(object sender, EventArgs e)
{
textBox1.Text = string.Join("\r\n\r\n", upv.ParcelList);
textBox1.AppendText("\r\n\r\n\r\n");
textBox1.AppendText(upv.ToString());
}