[tex]\bf Step-by-step~explanation:[/tex]
[tex]\bf Step~1:[/tex]
To solve this, we have to simplify these numbers by adding like terms.
[tex]42x^2+34-8-12\\\\(34-8=26, 26-12=14)\\\\42x^2+14\\[/tex]
[tex]\bf Step~2:[/tex]
Next, we factor our expression. To do so, we look for the greatest common factor of 42 and 14, which is 14. We know that because 42 divided by 14 is 3.
[tex]\frac{42}{14} =3[/tex]
[tex]\boxed{ \bf Our~final~answer: 14(3x^2 + 1)}[/tex]