Rewrite $ 16m^2-p^2 $ as:
$$ \color{blue}{ 16m^2-p^2 = (4m)^2 - (p)^2 } $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = 4m $ and $ II = p $ , we have:
$$ 16m^2-p^2 = (4m)^2 - (p)^2 = ( 4m-p ) ( 4m+p ) $$