Solve by substitution method: 3x - 4y =20, x+2y= 5
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3x-4y=20
or, 3x=20+4y
or, x=(20+4y)/3
x+2y=5
or, (20+4y)/3+2y=5
or, (20+4y+6y)/3=5
or, 20+10y=15
or, 10y=15-20
or, y=-5/10
or, y=-1/2
then, x=(20+4y)/3={20+4*(-1/2)}/3=(20-2)/3=18/3=6
required solution, x=6,y=-1/2
or, 3x=20+4y
or, x=(20+4y)/3
x+2y=5
or, (20+4y)/3+2y=5
or, (20+4y+6y)/3=5
or, 20+10y=15
or, 10y=15-20
or, y=-5/10
or, y=-1/2
then, x=(20+4y)/3={20+4*(-1/2)}/3=(20-2)/3=18/3=6
required solution, x=6,y=-1/2
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