1) 4.3/7-1.9/14=(4-1)+(3/7-9/14)=3.6-9/14=2.14+6-9/14=2.11/14

2) 7,8: 2.11/14=7.8/10:2.11/14=78/10:39/14=78/10*14/39=14/5=2.4/5

3) 2.4/5+0,312= 2.4/5+312/1000=2.800+312/1000=2.1112/1000=3.112/1000 сокращаем на 8  = 3.14/125

4)3.14/125*(-5.5/10)=3.14/125*(-5.5/10)= 389/125*(-55/10)=-4279/20=-217.9/20