A new observation of mathematics in the first volume of the seventh grade, page 34, the answer to the eighth question and the third question
It's very clear to draw a coordinate map. Let B=x, then A= 1+x, and C= -(3-x)=x-3. Substitute A+B+C=0 and get x=2/3. Therefore: A=5/3, B=2/3, C=-7/3. So -A? 0? 5+2B-C-(A-4C-B)= -85/9. You can do some more calculations to see if it is correct.