Answer
$$-65$$
Work Step by Step
In order to solve this problem, we follow order of operations. (Recall, we use the abbreviation PEDMAS to indicate the correct order.) Doing this, we find:
$$ 12-100\div \:5\left(-2\right)^2-3\left(-1\right)\\ 12-80-3\left(-1\right)\\ 12-80-\left(-3\right)\\ -65$$