i checked a book out of the library entitled coles notes how to get an A in senior algebra, the very first chaptor is on factoring, so i assume that this belongs here, at the end of the chapter are a few questions pertainng to the chapter, one question that i am having trouble with is:

ad-3bd-ab+3b^2+ac-3bc

the anwser is (a-3b)(d-b+c)

i need to know step-by-step how the book arrived at the anwser, so that i can solve similar equations myself.