Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.3 - Integers: Addition and Subtraction - Problem Set 1.3 - Page 19: 43

$-45$

We start with the given expression: $-18-27$ First, we will convert this to an addition problem: $-18+(-27)$ To find the sum of two negative integers, we simply find the sum of their absolute values and attach a negative sign. $-18+(-27)=-(|-18|+|-27|)=-(18+27)=-45$