Ответ:

(3 5/6 +а)-2 1/6=5

3 5/6 +а- 2 1/6=5

а=5-3 5/6 + 2 1/6= 5-3 2/3=15-11/3=4/4=1 1/3

 

8 6/13- (b+9/13)=4 2/13

8 6/13- b-9/13= 4 2/13

-b=4 2/13-8 6/13+9/13

-b= -4 6/13+9/13=-58/13+9/13=-49/13=-3 10/13

b= -3 10/13 : -1

b= 3 10/13