1) (-12,4+8,9)*1 3/7= -3,5*1 3/7=-35/10*10/7=-35/7=-5
2) (-0,76-0,44):2 2/3= -1,5:2 2/3=-15/10*8/3=-20/5=-4
3) (2 3/8-1 5/6):(-1 5/8)= (19/8-11/6):(-1 5/8)= 13/24:(-13/8)=-1/3
4) (3 5/14- 2 3/4)*(-3 5/17)=(47/14-11/4)*(-56/17)=(94/28-77/28)*(-56/17)=17/28*(-56/17)=-56/28=-2