where is /4 coming from?? how can you just divide by 4 like that?!

factor out -4, you get

you're using the ac method, so i will as well. here ac = -40 and b = 6, so think of two number that when you multiply them you get -40, but you add them and get 6. 10 and -4 works. so split the middle term into those two, you have:

now factor what's inside the brackets using "factor by grouping"