[tex]\sf\purple{A.\:(m\:+\:4n) \:(m\:-\:7n) }[/tex] ✅
[tex] {m}^{2} - 3mn \: - {28n}^{2} \\ = {m}^{2} + 4mn - 7mn - {28n}^{2} \\ = m \: (m + 4n) - 7n(m + 4n) \\ = (m + 4n)(m - 7n)[/tex]
[tex]\circ \: \: { \underline{ \boxed{ \sf{ \color{green}{Happy\:learning.}}}}}∘[/tex]