Answer
$18a^{2}-11ab-10b^{2}$
Work Step by Step
Use FOIL:
First:$\quad (9a)(2a)=18a^{2}$
Outer:$\quad (9a)(b)=+9ab$
Inner:$\quad (-10b)(2a)=-20ab$
Last:$\quad (-10b)(b)=-10b^{2}$
Outer and Inner parts produce like terms, whose sum is $-11ab$
$=18a^{2}-11ab-10b^{2}$
