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Posted by **lovey** on Sunday, February 21, 2010 at 12:51am.

3x + 12 = -7x - 28

I know the answer is x = -4

and I know that substitution is the technique that is used, but I can't figure out how to set this up

- algebra -
**Marie**, Sunday, February 21, 2010 at 1:09am3(-4) + 12 = -7(-4) - 28

-12 + 12 = 28 - 28

0 = 0

- algebra -
**Reiny**, Sunday, February 21, 2010 at 7:44am3x + 12 = -7x - 28

Add 7x to both sides

3x + 12 + 7x = -7x - 28 + 7x

10x + 12 = -28

Now subtract 12 from both sides

10x + 12 - 12 = -28 - 12

10x = -40

now divide both terms by 10

x = -4

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