text: # Use the .append() method to combine the tracks tables
  metallica_tracks = tracks_ride.append([tracks_master, tracks_st], sort=False)
  
  # Merge metallica_tracks and invoice_items
  tracks_invoices = metallica_tracks.merge(invoice_items, on='tid')
  
  # For each tid and name sum the quantity sold
  tracks_sold = tracks_invoices.groupby(['tid','name']).agg({'quantity':'sum'})
  
  # Sort in decending order by quantity and print the results
  print(tracks_sold.sort_values(['quantity'], ascending=False))