We have the following expression:
[tex]18a^4w+168a^2bk-72a^4k-42a^2bw[/tex]Lets find the greatest common factor of all terms. We can note that the gcf of the number is
[tex]\begin{gathered} \text{the factors of 18 are: }1,2,3,6,9,18 \\ Thefactorsof42are\colon1,2,3,6,7,14,21,42 \\ Thefactorsof72are\colon1,2,3,4,6,8,9,12,18,24,36,72 \\ Thefactorsof168are\colon1,2,3,4,6,7,8,12,14,21,24,28,42,56,84,168 \end{gathered}[/tex]They have in common the number 6, then we can rewritte our expression as:
[tex]6(3a^4w+28a^2bk-12a^4k-7a^2bw)[/tex]Regarding the variables, we can note that the term
[tex]a^2[/tex]is in all the terms of our expression, then we have
[tex]6a^2(3a^2w+28bk-12a^2k-7^{}bw)[/tex]