Step-by-step explanation:
[tex]28 = 2 \times 2 \times 7 \\ 42 = 2 \times 3 \times 7 \\ 56 = 2 \times 2 \times 2 \times 7 \\ \\ common \: factors = 2, \: 7 \\ \\ greatest \: common \: factor \\ = product \: of \: common \: factors \\ = 2 \times 7 \\ = 14[/tex]
