(0.4k3 – 2.5k) – (2.4k3 + 3k2 – 1.2k) =

Distribute the minus sign across the second parentheses: 0.4k³ − 2.5k − 2.4k³ − 3k² + 1.2k. Combine like terms: (0.4 − 2.4)k³ = −2k³, and (−2.5 + 1.2)k = −1.3k, leaving −3k². The result is −2k³ − 3k² − 1.3k, choice C.

AI-written and checked against the verified answer.