(3.5/6+a)-2.1/6=5, 8.6/13-(b+9/13)=4.2/13
3.5/6+а=5+2.1/6 3.5/6+a=7.1/6 a=7.1/6-3.5/6 a=3.1/3 *** b+9/13=8.6/13-4.2/13 b+9/13=4.4/13 b=4.4/13-9/13 b=3.8/13
Спасибо