17 3/15-8 7/20-4 16/60= 17 12/60-8 21/60-4 16/60= 5 12/60-21/60-16/60=4 72/60 - 21/60 - 16/60= 4 35/60 =4 7/12
17 3/15-8 7/20-4 16/60= 17 12/60-8 21/60-4 16/60= 5 12/60-21/60-16/60=4 72/60 - 21/60 - 16/60= 4 35/60 =4 7/12