Answer:
-7r^3 - r^2 +7
Step-by-step explanation:
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[tex](r^3-9r^2+3r)-(8r^3-8r^2+3r-7)=\\\\=r^3-9r^2+3r-8r^3+8r^2-3r+7=\\\\=r^3-8r^3-9r^2+8r^2+3r-3r+7=\boxed{-7r^3-r^2+7}[/tex]
