To simplify the expression (3g-4)-2(3g+4), start by distributing the -2 to the terms inside the parentheses:
3g - 4 - 2 * 3g - 2 * 4
Simplify the expression:
3g - 4 - 6g - 8
Combine like terms:
(3g - 6g) + (-4 - 8)
-3g - 12
The simplified expression is -3g - 12.