г) -4m²(n² - m²) + 3n²(m² - n²).

Раскроем скобки и приведем подобные члены:

$$-4m^2(n^2 - m^2) + 3n^2(m^2 - n^2) = -4m^2n^2 + 4m^4 + 3n^2m^2 - 3n^4$$

$$= -4m^2n^2 + 3m^2n^2 + 4m^4 - 3n^4 = -m^2n^2 + 4m^4 - 3n^4$$

Ответ: $$4m^4 - m^2n^2 - 3n^4$$