Which of the following is a factor of xy + 3y + 7x + 21?

To determine the factors of the expression xy + 3y + 7x + 21, we can group the terms in pairs:

• (xy + 3y) + (7x + 21)

Now, we can factor out the common terms from each pair:

• y(x + 3) + 7(x + 3)

Next, we can notice that both groups contain a common factor of (x + 3):

• (x + 3)(y + 7)

Thus, we can conclude that (x + 3) and (y + 7) are factors of the original expression xy + 3y + 7x + 21.