How to simplify this equation to a specific form? How can I simplify this expression? 
$$ 2(4^{n-1})-(-3)^{n-1} + 12 ( 2 (4^{n-2})-(-3)^{n-2})$$ 
The correct answer is $2 · 4^n − (−3)^n$

hint:
use the fact that
$$a^n = a\cdot a^{n-1}$$
and that
$$a^n = a^2\cdot a^{n-2}$$
