The answer is -14x + 1.
(10 - 5x) - (9x + 9) | the operators switched to the opposite: from - to +
(10 - 5x) - 9x - 9
-5x + 10 - 9x - 9
-14x + 1
10-5x-9x+9
19-5x-9x
19-14x
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