<PRE><B>Question 494372</B>
3x+3y=-9 ...........(1)
3x-3y=-21...........(2)

Add (1) and (2)
3x+3y=-9 
3x-3y=-21
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6x=-30
x=-30/6
x=-5
Put the value of x in either equations (1) or (2)
3x+3y=-9 ...........(1)
3(-5)+3y=-9
-15+3y=-9
3y=-9+15
3y=-9+15
3y=6
y=6/3
y=2

Solution Set (-5,2)

Check:
Put the value of x and y in either equations (1) or (2)
3x-3y=-21...........(2)
3(-5)-3(2)=-21
-15-6=-21
-21=-21




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