21 2/59-2/5*(3 15/28:9/27-1:1 10/49):2=
21 2/59-2/5*(99/84:9/27-1:59/49):2=
21 2/59-2/5*(99/28-49/59):2
1241/59-2/5*(5841/1652-1372/1652):2=
1241/59-2/5*(4469/1652):2=
1241/59 -2/5*4469/3304=
1241/59-4469/8260=
173740/8260-4469/8260=
169271/8260 = 20 4071/8260≈ 20,49