Выполните действие а) 10 4/15+9 11/15-8 1/30; б) 19 1/17-8 9/17-3 15/17; в на завтра !

А) 10 4/15 + 9 11/15 - 8 1/30 = 11 29/30 
1) 10 4/15 + 9 11/15 = 19 15/15 = 20
2) 20 - 8 1/30 = 19 30/30 - 8 1/30 = 11 29/30

б) 19 1/17 - 8 9/17 - 3 15/17 = 6 11/17
1) 19 1/17 - 8 9/17 = 18 18/17 - 8 9/17 = 10 9/17
2) 10 9/17 - 3 15/17 = 9 26/17 - 3 15/17 = 6 11/17

в) (6 7/12 + 8 5/12) - 7 16/21 - 4 6/21 = 2 20/21
1) 6 7/12 + 8 5/12 = 14 12/12 = 15
2) 15 - 7 16/21 = 14 21/21 - 7 16/21 = 7 5/21
3) 7 5/21 - 4 6/21 = 6 26/21 - 4 6/21 = 2 20/21