Answer
9$a^{2}$ +23ab-12$b^{2}$
Work Step by Step
(a+3b)(9a-4b) FOIL method
(a)(9a)+(a)(-4b)+(3b)(9a)+(3b)(-4b)
9$a^{2}$ -4ab+27ab-12$b^{2}$
9$a^{2}$ +23ab-12$b^{2}$
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