Chapter 1 - Foundations for Algebra - Chapter Review - 1-5 and 1-6 Operations with Real Numbers - Page 71: 64

$3$

To subtract, we add the opposite. Therefore, $-9-(-12)=-9+12$ To add numbers with different signs, we find the difference of their absolute values. Then, we use the sign of the addend with the greatest absolute value. Since -9 and 12 have different signs, we use this method: $(12-9)=3$