First pull out -1:
What we want to do now is apply the grouping technique:
However, we have to manipulate it in such a way so we can use it.
Note that -13*7=-91 and -24=39-63.
Now, let us rewrite the trinomial:
From the red group, factor out a 3q and from the blue group, factor out a -7.
Thus we now have:
Note that both terms have the same factor. Factoring out the blue term, we get:
Hope this makes sense!