13,4/9-(12,5/9-х)=4,3/9

1,49 - (1,39-x) = 0,48 ;
1,39-x = 1,49-0,48 ;
1,39-x = 1,01 ;
x = 1,39-1,01 ;
x = 0,38 ;
Ответ: x = 0,38.