12 1/2 + (17 1/2-8/5) :(11 2/3:7/9+0,6*10)=
=12 1/2 + 15 9/10 :(11 2/3:7/9+0,6*10)=
=2 1/2 + 15 9/10 :(15+0,6*10)=
=2 1/2 + 15 9/10 :(15+6)=
=2 1/2 + 15 9/10 :21=
=2 1/2+53/70=
=3 9/35
17 1/2-8/5=35/2-8/5=175/10-16/10=159/10=15 9/10
11 2/3:7/9=35/3:7/9=35/3*9/7=15/1=15
0,6*10=6
15+6=21
15 9/10 :21=159/10:21/1=159/10*1/21=53/70
2 1/2+53/70=5/2+53/70=175/70+53/70=228/70=3 18/70=3 9/35