г) $$(m^3 + n^3) - m(m^2 - mn + n^2) = (m + n)(m^2 - mn + n^2) - m(m^2 - mn + n^2) = (m^2 - mn + n^2)(m + n - m) = n(m^2 - mn + n^2)$$.
Ответ: $$n(m^2 - mn + n^2)$$.