To complete this algebra problem, just like any other, we have to complete the proper steps in order; here as follows.
1. −3x^2 + 20x − 12
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x - 6
2. (−3x + 2) (x − 6)
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x - 6
And finally..
You come up with the answer of:
-3x + 2
I hope this cleared up the little confusion you may have been having. If you need more information on the steps, just ask.