(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: 0.4k³ − 2.4k³ = −2k³, and −2.5k + 1.2k = −1.3k; the −3k² term stays unchanged. The result is −2k³ − 3k² − 1.3k, choice C.

AI-written and checked against the verified answer.