Final answer:
The expression -6m⁴ + 3m⁴ is simplified by combining like terms with the same variable part, which results in -3m⁴ after adding the coefficients of the terms together (-6 + 3).
Step-by-step explanation:
To simplify the expression -6m⁴ + 3m⁴ by combining like terms, you need to add the coefficients (numerical factors) of the terms that have the exact same variable part. In this case, both terms have the variable part m⁴. You combine -6m⁴ and 3m⁴ by adding their coefficients: -6 and 3.
-6 + 3 = -3
So, -6m⁴ + 3m⁴ simplifies to -3m⁴.