#### Answer

$a=-21/16$

#### Work Step by Step

The distributive property allows us to distribute anything multiplied by something inside of the parenthesis to whatever is inside of the parenthesis. Thus, we distribute the 3 to everything inside of the first set of parenthesis, the -2 to everything inside of the second set of parenthesis, and the 4 to everything in the third set of parenthesis, giving us the equation 6a-3-10a-2=12a+16. We now simplify:
$-4a-5=12a+16 \\\\ -5=16a+16 \\\\ -21=16a \\\\ a=-21/16$