Respuesta :

(3-a)(3a+4)(a-5)=
(9a+12-3a^2-4a)(a-5) =
(5a+12-3a^2)(a-5) =
5a^2-25a+12a-60-3a^3-15a^2 =
-10a^2-13a-60-3a^3 =
10a^2+13a+60+3a^3


hopefully this helps :)