Subtract 11b^2 - 4b + 7 from b^2 + 8b - 9 ?
That is
[tex]b^2+8b-9-(11b^2-4b+7)=b^2+8b-9-11b^2+4b-7[/tex]Collecting like terms we have
[tex]b^2+8b-9-(11b^2-4b+7)=b^2-11b^2+8b+4b-9-7=-10b^2+12b-16[/tex]Hence the result of the subtraction is
[tex]-10b^2+12b-16[/tex]