example:
given equations: B=3A C=A+30 180=A+B+C
Reorder equations so the variables match up. A +B+C=180 3A+B =0 A C=30
Add equations together so you can get rid of variables you might have to multiply an equation by a number to do this.
A+B+C=180 + A C=30  2A+B =150
Now subtract the unused equation.
2A+B=150  3A+B=0  5A=150 A=30
Now all you need to do is substitute 30 in for A and you can find the answer to the other equation then substite A and C in another equation and walla. A=30 B=90 C=60
