21 2/59-2/5*(3 15/28: 9/28-1: 1 10/49): 2

21 2/59-2/5*(3 15/28:9/28-1:1 10/49):2=19
по действиям

3 15/28=99/28
99/28:9/28=99/28* 28/9=11

1 10/49=59/49
1:59/49=1*49/59=49/59

11- 49/59=10 10/59=600/59

2/5:2=2/5* 1/2=1/5

1/5*600/59=120/59=2 2/59

21 2/59-2 2/59=19