11 3/14 - (2 - 1 11/35) : 9/25 + 4/21 = 9 20/21
1) 2 - 1 11/35 = 1 35/35 - 1 11/35 = 24/35
2) 24/35 : 9/25 = 24/35 · 25/9 = (8·5)/(7·3) = 40/21 = 1 19/21
3) 11 3/14 - 1 19/21 = 11 9/42 - 1 19/42 = 10 51/42 - 1 19/42 = 9 32/42 = 9 16/21
4) 9 16/21 + 4/21 = 9 20/21