Answer: c < -13
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Work Shown:
9c + 90 < -27
9c + 90 - 90 < -27 - 90 .... see note 1
9c < -117
9c/9 < -117/9 ... see note 2
c < -13
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note 1: I'm subtracting 90 from both sides to undo the "plus 90" that is happening on the left side
note 2: I divided both sides by 9 to undo the multiplication. The expression 9c is the same as 9*c or "9 times c". The inequality sign will not flip as we are dividing both sides by a positive number.