The answer is: [A]: " 20a − 5b − 9 " .
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Explanation:
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(12a + 7b) + (−6a − 9) + (14a − 12b) =
12a + 7b + 1(−6a − 9) + 1(14a − 12b) =
12a + 7b + (1*-6a) + (1*-9) + (1*14a) + (1* -12b) =
12a + 7b − 6a − 9 + 14a − 12b = ?
Combine the "like terms:
12a − 6a + 14a = 20a ;
7b − 12b = - 5b ;
and then we have "-9" ;
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So, write as: " 20a − 5b − 9 " ; which is: Answer choice: [A].
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