The first two terms have 2x in common, which we can factor out to find 2x(x + 7) - 3x - 21. For the second two terms, we could factor out 3 or we could factor out - 3. Whoa! Rein in your pony there, cowboy. If we factor out 3, we'll find 2x(x + 7) + 3(-x - 7). Those two terms don't have a common factor. Instead, if we had factored out - 3 we would get 2x(x + 7) - 3(x + 7) and we could pull out (x + 7) to see that (2x - 3)(x + 7). | 
Calculator