20+5m+12n+3mn

Group the first two terms and the last two terms.

(20+5m)+12n+3mn

Factor out the greatest common factor (GCF) from each group.

5(4+m)+3n(4+m)

5(4+m)+3n(4+m)

Factor the polynomial by factoring out the greatest common factor, 4+m.

(4+m)(5+3n)

Factor by Grouping 20+5m+12n+3mn