Answer
$24a^{3} +28a^{2}b-6a-7b$
Work Step by Step
$(2a+1)(2a-1)(6a+7b)$
Multiplying $(2a+1)(2a-1),$ it is in the form of $(a+b)(a-b)$
$(a+b)(a-b)= (a^{2}-b^{2})$.
$(2a+1)(2a-1)=(2a)^{2}-1^{2} = 4a^{2} - 1$
$(2a+1)(2a-1)(6a+7b) = (4a^{2} - 1)(6a+7b)$
$=24a^{3}+28a^{2}b-6a-7b$
