(2.39-1.79)+ 6.49 -(4.29+89) 

 ( 2 3/9 - 1 7/9 ) + 6 4/9 -  ( 4 2/9 + 8/9 ) =

 2 3/9 - 1 7/9 = 21/9 - 16/9 = 5/9

5/9 + 6 4/9 = 5/9 + 58/9 = 63/9 = 7

4 2/9 + 8/9 = 38/9 + 8/9 = 46/9 = 5 1/9

7 - 5 1/9 =  7/1 - 46/9 = 63/9 - 46/9 = 17/9 = 1 8/9

(2.39-1.79)+ 6.49 -(4.29+89)=1,8/9

1) 2.39-1.79=5/9

2) 5/9+6,4/9=7

3) 4,2/9+8/9=5,1/9

4) 7-5,1/9=1,8/9