12.

 

7x^2+29x+24

Here it is not quite so obvious how to break the middle term up

to recover the O and I terms. But if we multiply the first and last

coefficients, and survey all possible ways to multiply two number to

get that product,

 

Factors of 168

 

and we find a pair of numbers that will work:

 

7x^2+21x+8x+24

 

which comes from

 

(7x+8)(x+3)

 

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