Answer
$-6.6x^2-1.8x-1.8$
Work Step by Step
$(1.2x^2 -3x+9.1)-(7.8x^2 -3.1+8)+(1.2x-6)$
$=1.2x^2 -3x+9.1-7.8x^2 +3.1-8+1.2x-6$
$=1.2x^2 -3x+9.1-7.8x^2 +3.1-8+1.2x-6$
$=-6.6x^2-1.8x-1.8$
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