(3\4-4\5)*7,8+(2\3+4\7)*7\13  СРОЧНО!!!!!!!!!!!!

(3//4-4//5)*7,8+(2//3+4//7)*7//13=(0.75-0.8)*7.8+(2//3+4//7)*(7//13)=(-0.05)*7.8+(2//3+4//7)*(7//13)=-0.05*7.8+(2//3+4//7)*(7//13)=-0.39+(2//3+4//7)*(7//13)=-0.39+26//21*(7//13)=-0.39+2//3=83//300 (~0.27)

// - черта дроби

(3/4-4/5)*7,8+(2/3+4/7)*7/13=83/300

3/4-4/5=-1/20

-1/20*7,8=-1/20*7 8/10=-1/20*78/10=-39/100

2/3+4/7=26/21

26/21*7/13=2/3

-39/100+2/3=83/300