3. 12a-10b-10a+6b=2a-4b;
4(3x-2)+7=12x-8+7=12x-1;
8x-(2x+5)+(x-1)=8x-2x-5+x-1=7x-6

1. 12*(-3/4)-3*5/6=-9-5/2=-11(1/2)