The given expression is
[tex]8n^2-2mn-3m^2+12mn[/tex]Let's group the terms in order to factor out the greatest common factor of each
[tex](8n^2-2mn)+(-3m^2+12mn)[/tex]Notice that the greatest common factor in the first binomial is 2n, and the greatest common factor of the second binomial is 3m. Let's factor them out
[tex]2n(4n-m)+3m(-m+4n)=2n(4n-m)+3m(4n-m)[/tex]As you can observe, 4n-m is a common factor, so we have to factor it out too
[tex](4n-m)(2n+3m)[/tex]