Very difficult!

Select the right operation


../sonsmp3/sixteen.mp3

../sonsmp3/twenty.mp3

../sonsmp3/seventeen.mp3

../sonsmp3/fourteen.mp3

../sonsmp3/twelve.mp3

../sonsmp3/ten.mp3

../sonsmp3/eighteen.mp3

../sonsmp3/fifteen.mp3

../sonsmp3/nineteen.mp3

../sonsmp3/thirteen.mp3