I need to know this quick

4(-4.2)^3 + 4(-4.2)^2 =???????

i know the answer is -225.79200 , but i keep getting 366.912 and its pissing me the fuck off because i have gone over it a million times and this is the only question out of all of them i have got wrong but i have no idea what i did wrong. so can some ne give me a quick little walk through, a mod can delete after i get an answer.

thanks!