To solve this expression, we need to follow the order of operations (PEMDAS/BODMAS).

First, we need to simplify the exponent: (-2)^3 = -2 * -2 * -2 = -8.

Now we can substitute this value back into the expression:

6 * (-8) + 5 * (-4) - (-12)

Next, we perform the multiplication:

-48 + (-20) - (-12)

To subtract a negative number, we can rewrite it as addition:

-48 + (-20) + 12

Now we can add the numbers together:

-48 + (-20) + 12 = -56

Therefore, the final answer is -56.