First we have to find the factor of each number
[tex]\begin{gathered} \text{factor}(28)=\lbrace1,2,4,7,14,28\rbrace \\ \text{factor(30)= }\lbrace1,2,3,5,6,10,15,30\rbrace \end{gathered}[/tex]after that, we should look for the factor in common, in this case we have in common 1 and 2. So the greatest common factor is 2
