Is that a -6 at the start? Let's assume so.
[tex]-6-7m^2 + 4n^2 - 8 - 9m^2 - n^2 [/tex]
We first group the like terms (same powers of the variables) together:
[tex] = (-6-8) +(-7m^2- 9m^2) + (4n^2 - n^2)[/tex]
Now we can add the like terms, kinda like we can add fractions with a common denominator:
[tex] = -14 -16m^2 + 3n^2[/tex]
That's the answer.
