(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