(–b3 + 3b2 + 8) – (? – 5b2 – 9) = 5b3 + 8b2 + 17? = –6b³–4b³4b³6b³

Distribute the subtraction across the second parentheses: subtracting (? − 5b² − 9) adds 5b² and 9. The known terms then combine to −b³ + 8b² + 17, so the equation is −b³ + 8b² + 17 − ? = 5b³ + 8b² + 17. Matching the b³ terms gives −b³ − ? = 5b³, so ? = −6b³, choice A.

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