Skills Handbook - Simplifying Expressions With Integers - Exercises - Page 975: 5

$-17$

Subtraction is the same thing as addition of a negative, so $-5-12=-5+(-12)$. To add two numbers with the same sign, we add their absolute values, and assign sum the same sign as both of the numbers: $$-5+(-12)=-(|-5|+|-12|)=-(5+12)=-17$$