1) -3,5+3/8+(-0,75)-1,1/4+(-6,7/8)=-12
1.-3,5+0,375=-3,125.
2.-3,125+(-0,75)=-3,875.
3.-3,875-1,25=-5,125.
4.-5,125+(-6,875)=-12.
2) 12,2+(-7,4)+(-4,5/6)+(-39,5)+50=11.
1.12,2+(-7,4)=48.
2.-4,5/6+(-39,1/2)=-43,8/6.
3.4,4/5+(-43,8/6)=-39,64/30.
4.-39,64/30+50=11.