Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.3 - Integers: Addition and Subtraction - Problem Set 1.3 - Page 20: 71

$-9$

The top number is $\text{ negative }$ and the bottom number is $\text{ positive .}$ Since the signs of the numbers are different, subtract the numbers and copy the sign of the bigger number. Hence, \begin{array}{r}\require{cancel} -18 \\\underline{\phantom{-1} 9 }\\ -9 \end{array}