Question 35967
THE FIRST SET SHOULD BE ADDED TO ELIMINATE THE Y TERM THUS 

3X-Y=21
2X+Y=4
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5X=25 OR X=25/5 OR X=5 THEN 3*5-Y=21 OR 15-Y=21 OR Y=-6 OR Y=6

THE NEXT SET MULTIPLY THE SECOND EQUATION BY 2 AND ADD (I ASSUME THE4 SHOULD BE FOLLOWED BY A Y)

3X+4Y=-10
10X-4Y=36 
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13X=26 OR X=26/13 OR X=2 THEN 3*2+4Y=-10 OR 6+4Y=-10 OR 4Y=-16 OR Y=-4

THE NEXT SET MULTIPLY THE FIRST EQUATION BY 4 AND ADD

8X-4Y=24
-3X+4Y=1
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5X=25 OR X-25/5 OR X=5 THEN -3*5+4Y=1 OR -15+4Y=1 OR 4Y=16 OR Y=16/4 OR Y=4

THE NEXT SET JUST ADD THE TWO EQUATIONS

X-Y=12
X+Y=22
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2X=34 OR X=34/2 OR X=17 THE 17-Y=12 OR -Y=-5 OR Y=5