Question 973583
(18n^3 + 42 n^2)  + (21n + 49)

6n^2(3n+7)   +  7(3n + 7)

Now combine the leading terms, since they are both multiplied by the same factor.

(6n^2 + 7) ((3n + 7)

When doing these, look for groups that will have either the same factor or the same if multiplied by minus 1  [ (x-7) and (7-x), for example]