Answer:
Option B. [tex]9x^{3}-2x^{2}-4x-2[/tex]
Step-by-step explanation:
we have
[tex]7x^{3}-2x^{2} +5[/tex]
[tex]2x^{3}-4x-7[/tex]
Adds the polynomial
Group terms that contain the same variable
[tex](7x^{3}+2x^{3})-2x^{2}-4x+(5-7)[/tex]
Combine like terms
[tex]9x^{3}-2x^{2}-4x-2[/tex]
Janice's error was
[tex]-2x^{2} +5-4x-7=6x^{2}-12[/tex]
so
[tex]-2x^{2}-4x=6x^{2}[/tex]
instead
[tex]-2x^{2}-4x=-2x^{2}-4x[/tex]
and
[tex]5-7=-12[/tex]
instead
[tex]5-7=-2[/tex]
