Factorize each of the following algebraic expressions:

$6(a+2 b)-4(a+2 b)^{2}$

$=[6-4(a+2 b)](a+2 b) \quad[$ Taking $(a+2 b)$ as the common factor $]$

$=2[3-2(a+2 b)](a+2 b) \quad\{$ Taking 2 as the common factor of $[6-4(a+2 b)]\}$

$=2(3-2 a-4 b)(a+2 b)$