We have a linear function
and we know that
Answer:
-9
Step-by-step explanation:
-2x + 3 = -x + 12
move -x over by adding
-x + 3 = 12
move the 3 over by subtracting
-x = 9
divide by - to get the x positive
x = -9
Hey!
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Formula: 
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Steps To Solve:
~Substitute

~Simplify

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Answer:

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Hope This Helped! Good Luck!