Factoring Polynomials

Algebra help (factoring polynomials)?
7(x - 4) + 28y(x - 4) factor completely if possible,
you can take x - 4 out but I think its prime. Very confusing.

7(x - 4) + 28y(x - 4)
Look for common factors to take out of the two terms.
The obvious being 7 and (x - 4).
If you divide both terms by 7(x - 4), you're left with (1 + 4y) in parentheses.
Therefore this equals 7(x - 4)(1 + 4y) 

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